American carrier strike groups

DEFENCE

Part 1 of 5

American Carrier Strike Groups: An Electronic Perspective

Fig. 1: A typical US Navy carrier strike group

A B. Kamalanath is a technical writer. He is also a research scholar, pursuing Ph.D in military technology

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n aircraft carrier is a moving airbase that can house approximately hundred combat aircraft. Being a ship, it can also sail to its war theatre quickly.

By remaining in international waters, it can launch punitive airstrikes on enemy targets. A combat aircraft can drop two tons of bombs in one go. So, hypothetically, 100 aircraft from a carrier can drop 200 tons of bombs on the enemy’s head, at a time.

A century ago, after the invention and eventual militarisation of the aircraft, somebody from the navy thought, “Why do we not operate aircraft from larger ships?” This idea led to the construction of a cantilever on a ship, from which the aircraft took off and landed on.

This resulted in the construction of dedicated aircraft-operating ships, which were called aircraft carriers or, simply, carriers. But these were not taken seriously, initially, and were used only as escorts or scouts to battleships, because during that era, combat aircraft itself was not considered an effective weapon altogether.

September 2015 | electronicS For You

This perception changed during World War II as Luftwaffe (German Air Force) taught damaging lessons to allied nations about the combat prowess of aircraft.

From the other side of the globe, Japan delivered a devastating aerial strike at Pearl Harbour using their carrier based aircrafts.

In one stroke, they almost entirely decimated the Pacific fleet of the US Navy (USN) but missed to destroy US navy’s carriers.

USN, after losing powerful battleships, had to retort to aircraft carriers as primary fighting weapons. It urgently assembled various ships to form taskforces with carriers as centrepieces and other ships to protect the carriers. These taskforces proved their mettle in the subsequent Battle of Midway and numbed the supremacy of Imperial Japanese Navy (IJN) in the Pacific.

From that instant, aircraft carriers took the driving seat in naval warfare.

Years after World War II, these taskforces morphed into formidable naval forces called carrier strike groups (CSGs). CSGs pack enormous strike power but, at the www.eFYmag.com

DEFENCE

Fig. 2: E-2C Hawkeye, AEW aircraft (top); F-18 combat aircraft in a typical strike load out (centre to wingtip): external fuel tanks, bombs, anti-radiation missiles and short-range air-to-air missiles (bottom)

same time, come with a sky-high bill.

For CSGs to survive and unleash their power, various electronic systems serve as the backbone. The electronic systems present in USN’s CSGs and how these play crucial roles are the subject of foci in this mil-tech article.

Defensive combat operations The purpose of a CSG is power projection; in simple words, launching combat aircrafts from the carrier stationed at deep seas and bombing the enemy. But the carrier being a highly-praised and priced target, objective of the enemy is to first destroy the carrier when the war begins. This could even turn the tide of the war.

Being a gigantic sitting duck on the sea, the enemy can easily find the carrier and attack either using aircraft, surface ships or submarines.

So, in order to protect the carrier, a CSG typically comprises four to six destroyers (a kind of warship), two cruisers (a larger warship) and a nuclear attack submarine.

Destroyers are highly specialised in defending the carrier from threats posed by enemy surface ships and submarines. These also have respectable capability against aircrafts.

Cruisers, which are slightly larger 72

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than destroyers, are specialised in taking care of enemy air threats. Due to a larger size, these possess more weapon capability than destroyers.

While destroyers operate at around 40km from the carrier to form a defensive perimeter against surface and sub-surface threats, cruisers operate in the vicinity of the carrier to provide air defence.

The two complement each other.

Through a myriad of sensors, these can detect and neutralise the threats arising from all directions. Nuclear submarines sail well-ahead of the carriers looking for enemy submarines and operate loosely bound to the carrier. All these vessels try to form an impenetrable virtual bubble around the carrier.

A CSG wages offensive air strike battles (strike warfare) on the enemy and, at the same time, wages defensive battles against enemy aircrafts, enemy submarines and enemy surface vessels.

Air defence warfare During World War II, in Battle of Midway, a group of aircrafts from the USN came directly above IJN carriers Soryu, Kaga and Akagi, and bombed these. This was the turning point of

War at Pacific and even of World War II. Losing these carriers in just minutes proved too crippling for Japan, which ultimately put an end to Japanese Empire’s naval supremacy in the Pacific in the days that followed.

This ultimately led to the defeat of the Empire of Japan itself.

In hindsight, the radar’s absence in Japanese carriers was the key.

Ship-borne radars were yet to be introduced in these carriers. So, American aircrafts were able to bomb Japanese carriers undetected. But American carriers had been fitted with ship-borne radars, using which these could detect Japanese aircrafts beforehand and launch their aircrafts to defend in the nick of time.

Now, desperate Japan was looking to neutralise American carriers. To do so, some Japanese pilots rammed their aircrafts, fully-loaded with bombs and fuel, into American carriers, in what is called Kamikaze Attack. All these modes of attacks served as lessons for USN. When it started its ambitious carrier building and operating programme, air defence was given utmost priority.

Further to cement the importance of air defence, the USSR (of which the present Soviet Union was a part) entered into the picture as the newfound adversary of the USA to fight Cold War, a war fought without pulling a shot. The USSR sensed the challenging supremacy of the American carriers and fielded the deadly adversary of the carriers, the cruise missiles.

Having been developed inspired

by Kamikaze aircrafts, cruise missiles offered a convenient means to attack a carrier. Earlier cruise missiles were just unmanned Kamikaze aircrafts.

From the cost perspective, a cruise missile costs a fraction of a carrier.

But it is a very viable weapon, capable of being launched from bomber aircraft, warships and submarines.

Incidentally, many of the early Soviet cruise missiles had nuclear warheads, sufficient enough to melt the entire steel present in the CSG. www.eFYmag.com

DEFENCE The Soviet scheme was to simultaneously launch these missiles from submarines and bombers against the carrier from very long distances.

Navigation computers of these missiles were programmed in such a way that all cruise missiles reached the carrier at the same time but from different directions. This was called the saturation cruise missile strike plan of the Soviet. Even if one cruise missile would hit the target, that would have been sufficient. This changed the situation in favour of the USSR. Air defence warfare capabilities of the CSG have been on constant updates and upgrades all these years.

Today, air defence systems of an American CSG can be termed as the most superior system in the world.

Protecting the CSG from cruise missiles and cruise-missile-launching aircraft is called air defence warfare.

Air defence operations are carried out in four phases.

Phase I: Fighter aircraft and AEW aircraft combo The first line of defence of the CSG is carrier-borne F-18 combat aircraft, which can operate far away from the carrier and shoot down enemy bombers before they launch cruise missiles. But these cannot find bombers quickly, because they do not know their exact location.

Onboard radars of F-18 aircraft can accurately scan specific sectors and specific altitudes but not all sectors and altitudes. To guide these towards incoming bombers, a dedicated airborne early warning (AEW) aircraft (also carrier-borne) is used.

These AEW aircraft, named E2, have huge radars. An inverted saucer-like structure on the top is the radome for the radar antenna.

Radome is a structure made of radiotransparent material to protect the radar antenna from the environment.

Inside this radome is the rotating antenna of the high-power UHF Doppler radar.

This radar can detect and track multiple threats on the sea and in www.eFYmag.com

Fig. 3: AN/SPS-49 radar antenna

the air. It can simultaneously and automatically detect and track 2000 targets, spread across the air and sea.

The aircraft keeps tab on an area of over twelve million cubic kilometres (three million cubic miles). Not only that, it can precisely track cruise missiles that fly low enough, as if skimming the water surface. Being a crucial component for the defence of the carrier, this radar is highly capable of resisting the jamming efforts of the enemy.

These aircraft maintain a surveillance patrol far away from the carrier and act as a command-and-control (C2) station. These see what the radars of the CSG cannot see. If AEW aircraft detect any enemy bombers at a long range, these communicate the same to the carrier through a data link. Immediately, F-18 combat aircraft from the carrier are scrambled. These take off and race towards incoming enemy bombers to intercept and stop these from launching deadly cruise missiles. When F-18 aircraft reach their area of responsibility, AEW aircraft vector these towards the threat. F-18s intercept and shoot down bombers. There are four such AEW aircraft on a carrier.

Phase II: Air search radars and fighter aircraft combo Air defence operations relying on this combination is a grave scenario. It occurs when the AEW aircraft itself has been shot down. This scenario is very much possible if the incoming enemy aircraft force is large. In

this case, CSG radars are the only means to detect enemy air targets. For this, the carrier has two air surveillance radars: a 2D radar and a 3D radar.

2D air-search radar.

A 2D radar gives the two dimensions of the target’s position: range and bearing of the target. 2D radar AN/SPS-49 operates in L band (851MHz– 942MHz) and can detect air targets at a range of 463km (250 nautical-miles).

It can scan up to an altitude of 46km. A two-cavity Klystron oscillator is behind its peak power of around 350kW. Due to the thinness of the beam produced, it becomes difficult for the enemy to jam it.

Its antenna rotates at 6rpm to detect flying objects at longer ranges.

The flying object’s position is updated every ten seconds. When that flying object approaches further, the antenna rotates at 12rpm. Now, the flying object’s position gets updated every five seconds, which results in the target being tracked continuously.

This radar can simultaneously track 255 targets. Since it is sitting on the ship, it is subjected to the pitch and roll of the ship. To overcome this, the antenna is gyro-stabilised.

And because of this, even if the ship rolls to the side or pitches up or down due to the waves, this antenna stays where it was before the roll or pitch.

Through identify friend or foe (IFF) components organic to the radar, the targets’ friendliness is determined.

IFF shoots an ultra-short pulsecoded narrow beam of radar energy to the flying objects as a challenge.

The friendly aircraft through an IFF receiver receives this and responds with a suitable reply. The radar receives this reply and classifies the flying objects as friendly aircraft.

Now for the radar’s IFF challenge, if there is no proper reply from an airelectronicS For You | September 2015

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DEFENCE craft, it is assumed to be a hostile aircraft, and its course is continuously tracked. All air-surveillance radars of the CSG have IFF. 3D air-surveillance radar. If a target of interest appears, 3D radar AN/SPS-48 takes over. A 3D radar provides the range and bearing like the 2D radar but also provides the height of the target, which is an extra dimension of the target’s position.

Normally, to find the height of the target, a separate radar known as a height-finding radar (HFR) is used with the 2D radar. HFR’s antenna always nods up and down to direct the beams to find the height of the target.

But 3D radar is a computer-controlled planar-array radar that varies its frequency instead of nodding the antenna up and down. By changing the frequency of the transmitted RF energy, this radar radiates a series of pencil beams. If the transmitted frequency is increased, the beam travels down the face of the antenna, and vice versa. The radar computer keeps track of the frequencies as these are transmitted and detects when the target reflects these. Further, it converts returned frequencies into meaningful altitude data. For finding the range

Fig. 4: AN/SPS-48 radar antenna

and bearing, it simply rotates the antenna like a 2D radar.

Operating in the range of 2900MHz to 3100.5MHz (S band), a 3D radar can detect targets up to a range of 407km (220 nautical-miles) and heights up to 30km. It emits radar energy with a peak power of 2.2MW and an average power of 35kW. It has automatic detection and tracking capabilities to simultaneously detect and track multiple air targets. It also has a moving target

What is IFF and why is it necessary During wartimes, under combat stress, identification of friends among enemies becomes difficult. A significant portion of fatalities occur due to mistakenly identifying a friendly unit as enemy. This is called friendly fire.

A notable incident occurred during the 1971 India-Pakistan war. After inflicting terrible damage to Karachi Harbour, Indian missile boats withdrew deep into Arabian Sea. Combat aircraft of Pakistan Air Force searching for these saw a warship and engaged it. But to the horror of both parties, that ship was a Pakistani warship searching for escaped Indian missile boats.

Identifying friends is important but, at the same time, enemies also have to be identified.

During World War II, in Battle of Coral Sea, American combat aircraft intercepted some Japanese carrier based aircraft and shot down many of these. Remaining Japanese aircraft withdrew and headed for their carriers. These used radio direction finders (RDFs) to pin-point the location of their carriers.

In an RDF, there is a transmitter in the carrier continuously transmits a signal. The aircraft has a radio, which detects this signal and gives the exact direction of the transmitter.

Japanese aircraft were flying back in the evening towards their carriers. Unfortunately, unknown to them, Japanese transmitter’s frequency was very close to that of the Americans.

When the Japanese saw a carrier, they flew right beside it. The carrier flashed signal lights to the aircraft in an effort to confirm their identity. To the horror of the Japanese, it was an American carrier and not Japanese. The men in the carrier saw that those aircraft were not responding. This turned into a nightmare for the Americans as they realised that those were Japanese aircraft and not theirs.

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indicating (MTI) capability, which helps distinguish between moving targets from stationary targets. Hills or a landmass produce radar echoes, which is landmass clutter. In the radar-signal-processing circuitry, echoes from stationary features are attenuated. The resultant echo is of the moving targets.

Radar AN/SPS-48 is electronically-stabilised instead of gyro-stabilised. To compensate for the pitch and roll of the ship, the frequency emitted is changed to compensate it.

This is similar to the height-finding technique.

Using this tracking data, fighter aircraft can be scrambled towards incoming threat to intercept it. The carrier constantly updates the aircraft with the target’s location until interception, through datalinks.

However, if the enemy aircraft has launched its cruise missiles, the cruise missiles become the target.

Engaging the cruise missile through the fighter aircraft becomes difficult.

So, air defence warfare progresses to Phase III and is carried out through surface-to-air missiles (SAMs) of the CSG. Phase III and phase IV of air defence operations will be covered in next part of this article.

To be continued next month www.eFYmag.com

DEFENCE

Part 2 of 5

American Carrier Strike Groups: An Electronic Perspective

T B. Kamalanath is a technical writer. He is also a research scholar, pursuing Ph.D in military technology

he first part of this article in September issue covered defensive combat operations, air defence warfare, fighter aircraft and AEW aircraft combo (phase I), and air search radars and fighter aircraft combo (phase II). Read on:

Phase III: Operations: Aegis accompaniments Destroyers and cruisers associated with the carrier are called Aegis ships, which are equipped with a robust command and control (C2) system called Aegis. These ships are more potent due to the presence of superior radars and C2 systems, which are based on high-performance computers.

Aegis cruisers are well-suited to conduct air defence warfare due to their superior array of radars. These have 2D long-range air-search radar AN/SPN-49, which is also present in the carrier. This radar is followed by passive electronic phased array radar AN/SPY-1.

Aegis destroyers do not have AN/SPN49 radar. Hence, these cannot detect threats

Fig. 5: SM-2 missile being launched from Aegis cruiser

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from a long range. Aegis cruisers with AN/ SPN-49 radars detect threats at a long range and then Aegis C2 system lets the threats of interest to be tracked by AN/SPY-1 radar.

AN/SPY-1 multi-functional radars.

These are phased-array radars, which are the latest-generation radars that were introduced in the 1980s and are still state-ofthe-art. These have antennae composed of many transmitting and receiving (T/R) elements. Each element radiates and receives RF energy individually, a sort of many tiny antennae arranged into one big antenna.

A single source supplies RF energy to all T/R elements through computer-controlled phase shifters.

The radar computer controls the direction of the beam by varying the phase of the RF signal emitted by each T/R element. In time-domain analysis, the signal to each T/R element is delayed for a certain duration by these phase shifters. By suitably varying the phase (suitably delaying), a wavefront of electromagnetic energy is formed in the desired direction. In simple words, a beam is formed. A moving beam is formed by varying the phase accordingly. This technique is called electronically slewing the beam, in contrast to mechanical slewing.

In mechanically-slewed radars, position of the beam is constant with respect to the antenna. So the antenna itself must be slewed for scanning targets. The ability to slew rapidly is called agility. For rapid scanning requirements, the antenna must be slewed rapidly. But there are mechanical limitations beyond which the antenna cannot be slewed.

In AN/SPY-1 phased-array radar, the beam-formation technique provides agility for rapid slewing. Since the phase is varied by a computer, the direction of the beam can be switched in microseconds; there is no need for the antenna to move at all.

Because of this, the antenna of this radar is www.efymag.com

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Fig. 6: Launchers in Aegis destroyer (top) and Aegis cruiser (bottom)

not fixed in any mast but embedded on the superstructure of the vessel itself.

Using this technique, many individual beams can be formed depending upon the requirement for various functions, with each beam performing a specific function like scanning, tracking or providing datalinks. A single radar antenna covers a 90° sector in the azimuth and from the horizon in the front to the zenith overhead in elevation.

There are four antennae for this radar to cover a total of 360°. In this arrangement, a hemisphere of RF energy is maintained around the ship up to a range of around 185km (100-nautical-miles). The radar’s peak power is 4MW to 6MW and average power of 58kW in the S band.

Next in the line are the missiles for engaging the target.

SM-2 SAMs. The surface-to-air missile (SAM) used in Aegis vessels is called Standard Missile-2 (SM-2).

Its range is quite long and current versions are capable of engaging targets even up to 200km. The guidance scheme of SM-2 is a semi-active radar-guidance scheme. www.efymag.com

Generally, due to the long range involved, majority of long-range SAMs have semiactive radar-guidance schemes.

This means that these do not have radar transmitters but only radar receivers. These can only receive radar echoes but not chirp out radar signals like usual radars. These depend on other radars for guiding these to intercept the target.

Due to the longer engagement range, more radar signal strength is required to look for the target. For more signal strength, the missile must have ultra-strong batteries to pump enough amperes into the radar.

But ultra-strong batteries are heavy and consume more space in the missile. This extra weight introduces restrictions in the missile’s manoeuvrability.

Due to these reasons, the missile only has the radar receiver section as the target seeker. As reception does not involve huge power requirements, the receiver fits snugly into the requirement. The ship, which launches the missile, provides radar energy through an illumination-/ fire-control radar. This radar does not chirp out pulses but continuously focuses its high-energy radar signals on the incoming target. Reflected energy is picked up by the missile seeker.

The missile’s guidance system understands the position of the target due to the directional property of this received radar energy. Then, the guidance system aligns the missile for successful interception and intercepts the target to destroy it.

In Aegis cruisers and destroyers, SM-2 missiles are stored in a vertical launching system (VLS), which can hold 122 missiles in total and those present in destroyers can hold 96 missiles.

VLS is a generalised launcher system and can launch many types of missiles. Though depending on mission requirement, various types of missiles could be loaded to this VLS. Electronics For You | October 2015

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DEFENCE shares illumination radars for a large number of targets to neutralise simultaneous cruise-missile strikes.

The number of targets that could be engaged through this feature is kept as classified information. But without this time-sharing feature, the number of targets intercepted will be equal to the number of fire-control radars.

Cooperative engagement capability, the latest trend

Fig. 7: Antennae of AN/SPY-1 and AN/SPG-62 radars in Aegis cruiser (left) and Aegis destroyer (right)

For complex missions, entire VLS could be loaded with SM-2 missiles.

AN/SPG-62 illumination-/firecontrol radars. This radar operates in I/J NATO frequency band (8GHz20GHz) with a peak power of approximately 10kW. It is a continuous-wave illumination radar and does not chirp out signals as pulses. Instead, it focuses its energy as a fine pencil beam on the target, like focusing a flashlight on an object. Due to this, this radar is called an illumination radar.

In military parlance, this is known as painting the target. This radar is mechanically turned to steer the beam. There are four such radars in Aegis cruiser; two are rearward-facing and two are forward-facing. This arrangement provides 360° coverage.

With each radar illuminating a target, these radars can illuminate up to four targets.

Aegis destroyers have three of these radars and the absence of AN/ SPN-49 radar leaves it with lower air defence capability. This makes Aegis cruisers a prime node in the air defence architecture of CSG defending against cruise missile strikes.

Typical engagement sequence In the engagement sequence, first, incoming target is detected through AN/SPN-49 surveillance radar. Aegis C2 system directs that target to be 54

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tracked by AN/SPY-1 radar. From this tracking, the target’s trajectory is derived in Aegis C2 system and the target’s future course is computed.

Then, the point of interception is calculated, which is a place where the target can reach in a few moments.

SM-2 SAM is launched to reach this interception point through midcourse guidance.

Due to the very long range involved, the parent vessel gives commands for the missile to fly, which is called midcourse guidance. These commands are supplied through a datalink, typically a radio channel.

The missile receives this information through the datalink and flies accordingly. AN/SPY-1 radar provides this datalink too.

By the time SM-2 approaches incoming target, Aegis C2 system directs the fire-control radar to illuminate the incoming target. When the missile reaches an optimum distance from the target, it starts using its radar receiver and guides itself towards the target.

AN/SPY-1 allows many such beams to be formed. Because of this, many datalink channels can be established so that many SM-2 missiles can be given guidance commands.

This enables many missiles to stay on air to intercept the same target or multiple targets.

Similarly, Aegis C2 system time

As the CSG’s cruise missile defences increased in capability, the Soviets fielded faster cruise missiles; some of these cruise missiles were even capable of covering a kilometre in a second. Because of this high speed, reaction time for the CSG decreased to a great extent. Windows of interceptions also reduced for the CSG against these faster cruise missiles.

The Soviets also increased the range of cruise missiles. They augmented the number of cruise missiles carried by cruise-missile-carrying platforms. Soviet submarines, surface vessels and bombers were able to carry more cruise missiles in a compact manner. So, more number of cruise missiles of lethal speed could be fired from longer range and also in greater numbers.

Though Soviet Union is defunct now, Russian Federation and China have this cruise missile strike capability. To defend from this renewed attack of fury, American CSGs needed a new deal in cruise missile defence.

Cooperative engagement capability (CEC) is the new sinister air defence scheme of USN. Ironically, CEC has not been achieved through addition of any new radars or weapon systems but by sharing these.

Through this sharing, the capability level of air defence has increased exponentially. This is the first step towards a futuristic warfare called network centric warfare (NCW).

In CEC, tracking data from radars present in the destroyers and cruisers is shared using identical algorithms.

Each ship tracks a target with a radar and, simultaneously, sends this data www.efymag.com

DEFENCE to other ships. Each individual ship receives data and fuses it with its own radar data. This is carried out by employing high-capacity parallelprocessing computers and advanced fusing algorithms. The result is that, all individual ships see a common air defence scenario called air picture.

Earlier a destroyer or a cruiser could view the threat scenario on the air around it. But through CEC, the same vessel can now see the threat scenario on air around the entire CSG. The backbone of CEC is a robust communications system, which is jam-resistant and utilises the advantages of GPS. Ships communicate in pairs in 500MHz to 1000MHz band during short transmit/receive periods to a line-of-sight (radar) distance.

Data thus sent across the net is in near real-time, and communication is virtually jam-proof because of superior jam-resistant features.

The single greatest advantage is that a ship may not be seeing an incoming cruise missile through its radar, but can launch and guide a SAM to intercept the incoming cruise missile based on fused track data sent by other ships. Similarly, a ship may launch a SAM with another ship providing midcourse guidance with yet another ship illuminating the target.

For example, a single ship’s radar may be able to detect a cruise missile at 40km from the ship. If the cruise missile is travelling at a speed of 1mach (330m/s), then it will reach the ship in 120 seconds. So the ship has to intercept the incoming missile within two minutes to prevent sinking.

Assume that there are two CEC equipped ships, A and B, operating 40km apart on a straight line. Ship A detects a cruise missile at 40km from it along its axis and the cruise missile is flying towards ship B. Through CEC, as ship A detects the cruise missile, ship B also detects it. Now, the cruise missile has been detected at 80km from ship B against its 40kmdetection capability. Due to this, ship B now sufficiently has four minutes www.efymag.com

to intercept the missile. This feature greatly relieves the pressure on ship B, when it is operating near the shores.

With CEC, each individual ship is made to scan a specific sector and data from all ships is fused into a single air picture. Interestingly, two CSGs operating in close proximity can share the data. This enables both to have an overall air picture common for both strike groups.

Such capabilities have been achieved for the first time in history and even been deployed operationally.

Phase IV: Terminal air defence This phase is almost a cruise missile defence phase executed by the carrier, but can also tackle enemy aircraft, if at all enemy aircraft survive the previous air defence phases, which is a near impossible feat. But with cruise missiles, it is a different story.

Cruise missiles fly so low as if these are skimming over water surface. This flight profile helps these to hide among clutter, that is, echoes from the sea surface. With this flight profile, these may still escape interceptions carried out by Aegis vessels and reach the carrier, generally considered remotely possible. An enemy aircraft or cruise missile reaching this phase means that Aegis vessels have been neutralised.

For the carrier, there are two defensive lines against cruise missiles.

One is through Sea Sparrow SAM system and the other is through ship self defence system (SSDS). AN/APS-49 and AN/APS-48 radars of the carrier provide coordinates of the targets in the initial phase of engagement.

Evolved Sea Sparrow SAM system. Evolved Sea Sparrow is the name given to SAM. The entire system consists of a target acquisition radar called Mark-23 target acquisition system (TAS), an illuminator radar and missile launchers, all tied up to a fire control system (FCS) called Mark-91.

FCS is the point of man-machine interface. It is this FCS which has the FIRE switch to launch the missile.

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DEFENCE as a backup arrangement. There are four Mk-91 illuminators in a carrier.

In a saturation cruise missile strike against the carrier, there are many cruise missiles flying towards the carrier. There is a serious possibility that one or two cruise missiles escape interception from Sea Sparrow air defence envelope. The last resort is the ship’s self-defence system (SSDS).

The SSDS

Fig. 8: Elements of Sea Sparrow missile system

Missile launchers are situated at two places in the carrier; one is on the left side front of the carrier and the other is on the right or left side aft of the carrier. Each launcher carries eight missiles in ready-to-fire mode.

SAM, on the side of the incoming cruise missile, is fired to intercept the threat. Also, the carrier is manoeuvred so that more SAM launchers face the side from where maximum number of cruise missiles are incoming. This creates a crossfire area where two SAM systems can target the threats.

Evolved Sea Sparrow missile.

The evolved Sea Sparrow SAM has a semi-active radar-guidance system with midcourse datalink update scheme, like SM-2 SAM. It has an interception range of more than 50km.

Through AN/SPN-48 radar, highflying targets are identified and tracked. The engagement passes on to Mark-23 TAS. For low-flying cruise missiles, Mark-23 TAS directly comes into play.

Mark-23 TAS. Mark-23 is a 2D pulse-Doppler acquisition radar. It operates in 1GHz–2GHz (L band) and has been specifically designed to operate in high-clutter environments.

The radar can detect a target with a radar cross-section (RCS) as mini56

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mum as 1m at ranges around 40km.

Generally, cruise missiles have low RCS. The radar automatically starts tracking the fast-approaching cruise missiles.

This radar can also be used for aircraft traffic control in a secondary role. In this role, the range is around 185km.

This radar is gyro-stabilised and can tackle 30° pitches and rolls. It provides 360° coverage and up to 75° coverage in elevation. It rotates at 15rpm during normal azimuthal scanning. But under threat scenarios, it can rotate at 30rpm to track the target intensely. It can simultaneously track 54 targets. The desired target to be intercepted is chosen in the FCS. Then, illumination radars come into play being initiated by the FCS. Mark-95 illuminator. This radar operates in X band and produces 2kW average power. Generally, X band radiators are capable of producing a thin beam, which is essential for accuracy and resolution. This radar houses transmitter and receiver antennae separately. Cylindrical structures are radomes. Concave and convex radomes enclose receiver and transmitter antennae respectively.

Between these two is an electrooptical imager for electrooptical tracking,

SSDS is the second line of the carrier’s air defence. For a carrier there is a possibility of at least one incoming cruise missile in all eight directions during a saturation cruise missile strike. In this scenario, even a second lost in decision making implies destruction. So what claims importance here is prioritising threats and engaging these sequentially and, most importantly, quickly. For this, a decision-making automatic C2 system is required. SSDS is a system to neutralise these low-flying cruise missiles.

This is not a new system; it is simply a fibre-optic local area network (LAN) around an SSDS C2 system, connected with self-defence weapon systems like rolling airframe missile (RAM) and close-in weapon system (CIWS) called Phalanx, and sensors like long-range air-search radar AN/SPS-49, surface-search radar AN/SPS-67 and a centralised IFF system, and an electronic warfare suite.

The irony of SSDS is that, this integration in no way augments the individual system’s efficiency from its standalone capability. But integration reduces the reaction time during complicated cruise-missile-attack profiles. Data from all sensors are clubbed to form a single tactical picture in the computer. Tracks are analysed, threats are identified from the tracks. From here, threats are prioritised and finally engaged through a suitable weapon system.

For example, if two cruise missiles are approaching the carrier from different directions, the one closer to the carrier is given priority and engaged. www.efymag.com

DEFENCE uses; the operator chooses the settings accordingly.

AN/SPQ-9 air and surface surveillance radar. This is an air and surface s u r ve i l l a n c e X band-phased array radar. It covers 360° in azimuth at the rate of 30rpm.

This allows the radar to detect seaFig. 9: RAM missile being launched and radar elements of SSDS (inset) skimming missiles at the horizon Though this system is an auto- against the presence of heavy sea mated C2 system, it has a manual clutter. It automatically displays any override feature. For the commander, target with a relative speed exceeding SSDS suggests the mode of engage- ten knots. It complements high-altiment for incoming targets. In manual tude surveillance radars by detecting mode, it leaves the responsibility of missiles that are approaching just engagement to the operator. In au- above sea surface.

In surface mode, it generates a tomated mode, it takes care of the engagement itself. This automation separate surface frequency to detect reduces the time taken from detection surface targets. It can even detect a submarine that has partially subto engagement.

AN/SPS-49 long-range air-search merged and is just peeking its periradar. This radar can detect incom- scope above the water surface.

The radar is present in Aegis ing cruise missiles and aircraft flying very high but has restrictions in de- vessels also, where it helps these to fire accurately on the enemy surface tecting low flyers.

AN/SPS-67 surface-search/navi- vessels.

Rolling airframe missile (RAM). gation radar. This is a 2D radar that operates in 5450MHz to 5825 This missile is carried in bulk in its MHz region (G band). It is used for launcher. It is capable of reaching surface surveillance and navigation. mach 2 speeds with an effective This capability of the radar results range of 9km. It is independent of in it having a secondary capability of any radar and has a passive radardetecting low-flying cruise missiles. homing guidance. It targets the inThe radar’s detection range is around coming cruise missile by homing on 100km and it is capable of a peak its radar emissions.

Generally, anti-ship cruise missiles power of 280kW. It is flexible in a way that pulse have radars as seekers. RAM looks for widths and pulse-repetition frequen- radar emissions, finds these, locks on cies (PRF) of radar energy can be these and flies towards these. Also, varied, accordingly, for the desired RAM can target infrared (IR) emisresolution. A higher PRF setting and sions that are abundantly available in short pulse width increases the reso- the incoming cruise missile’s engine lution to detect two smaller targets exhaust. As the missile’s exhaust is in close proximity to each other. very hot, it emits IR radiations like a Other settings may even show these hot iron emitting red light.

Both Sea Sparrow and RAM have two targets as a single large target.

But other settings also have different a minimum range beyond only which www.efymag.com

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DEFENCE these can engage. These need time, at least a fraction of a second, to pick up maximum speed. The range at which these pick up maximum speed is their minimum range. It is highly difficult for RAM to manoeuvre towards the target before the minimum range with speed building up. If the incoming cruise missile escapes interception and closes in rapidly, air defence warfare progresses to close in defence.

Phalanx close-in weapon system (CIWS). CIWS is a rapid-firing Gatling gun. Gatling guns have rotating multiple barrels. Gatling gun, developed by Richard Gatling, was the first machine gun in the world.

In the past, the gunner had to rotate a crank handle to rotate the barrels in the first Gatling machine guns. But CIWS uses motors for this purpose.

At an astounding rate, CIWS shoots tungsten or depleted uranium tipped bullets. These bullets are known for their hardness, so the sheer number of these fired can literally shred incoming cruise missiles into pieces.

How does this last line of CIWS defence work? CIWS is generally kept as an independent and automatic system but with manual override features. It has its own set of radars, a search radar and a tracking-cumfire-control radar, to ensure last-resort air defence capability. For example, if SSDS connectivity is lost, CIWS can take care of missile defence.

These radars operate at 9200MHz9250MHz band and are capable of

Fig. 10: A CIWS firing

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Fig. 11: Air defence organs of the carrier highlighted; ESSM launcher and CIWS (left), Mk-91 illuminator radar (centre) and RAM launcher and CIWS (right)

emitting energy at a peak power of 1.4kW. The search radar keeps on scanning its sector around the carrier.

If a target appears, it gives the bearing, range and altitude of the target to the FCS of CIWS. FCS first checks if the target is approaching the carrier. If it is outbound, CIWS discards it. But if it is inbound, the track is taken as bogey (possible enemy). Now, FCS determines whether the bogey is in a collision course with the carrier by extrapolating the trajectory of the bogey through radar data. It also checks the speed of a bogey that presently is not in collision course. It does this to determine whether the target can manoeuvre to a collision course at a later stage.

If these assessments are positive, FCS instructs the tracking radar to start tracking the bogey. When the bogey reaches within the gun’s range, FCS commands the gun to start firing. Guns fire at a point where the bogey arrives in a few fractions of seconds. The tracking radar also tracks the trajectory of the bullets to check if these deviate due to any environmental parameters. If so, FCS fires the guns accordingly to offset the deviation.

Typically, CIWS first finds the targets at 8km from the carrier. If it detects that the target is inbound and flying between speeds of 140 knots and 1600 knots, it starts tracking the target at 5km. CIWS can detect and track a target flying at an altitude of 8km.

A typical USN carrier has three CIWS located strategically at the corners. So at any point of time, two CIWS can engage a single bogey to maximise the chance of destroying it. Each Aegis destroyer and cruiser has two CIWS to protect themselves.

Latest CIWS versions have EO sights (thermal imaging cameras) for the operator to distinguish a bogey from a friendly aircraft with his own eyes even in dark. Since CIWS does not have an inbuilt IFF, only SSDS supplies IFF data. So if SSDS connectivity is degraded, in automatic mode CIWS considers even a carrier-borne aircraft approaching to land as bogey and shoots it down.

Electronic warfare (EW) suite.

The EW suite is also integrated with SSDS to divert the missile by spoofing it. This spoofing attempt is the soft killing of the incoming missile. It may precede a SAM interception or take place along with the interception.

In the next issue we will discuss EW in detail.

To be continued next month www.efymag.com

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Part 3 of 5

American Carrier Strike Groups: An Electronic Perspective

T B. Kamalanath is a technical writer. He is also a research scholar, pursuing Ph.D in military technology

Fig. 12: EW module in a destroyer

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he first two parts of this article, published in September and October issues, covered air defence warfare in great detail. In this part we discuss electronic warfare (EW), under-sea warfare, surface warfare and strike warfare.

Electronic warfare EW is denying the enemy the advantage of using the electromagnetic spectrum effectively. In detail, the objective is to degrade the performance of the enemy’s communication and detection (radar) systems. This involves two operations, namely, detection and jamming/spoofing.

Detection is carried out through a scheme called electronic support measures (ESMs). This detects the enemy’s radar activity or their communication transmissions.

Jamming/spoofing is carried out through electronic counter measures (ECMs). This degrades the performance of the enemy’s radar activity and their communications. Through ESM, signals—be it radar or communication—are detected.

If an imminent attack is indicated, those

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signals are jammed through ECM. Both ESM and ECM are integrated into a single module called EW module. Two such separate modules are fitted in the carrier, one on each side. These two are tied up to an EW command console to give an overall scenario of emissions around the carrier.

Similarly, a set of EW modules is present in Aegis destroyers and cruisers.

Electronic support measures. There is an interesting and important property of radars. A radar is like a double-edged sword for the user. The ultimate intention of using it is to detect the enemy. How? A radar is like a flashlight used by an imaginary flycatcher to find a fly in a dark auditorium.

The flycatcher has to find the fly by waving the flashlight around. There is an effective range for the flashlight within which the fly catcher can find the fly.

But what will happen if the fly is beyond the effective range of the flashlight? The fly can easily find the presence of the flycatcher by seeing the dimly-lit flashlight. The flycatcher cannot find the fly at that distance but the fly can find the presence of the flycatcher. For this, the fly must have sensitive eyes, and that is all.

Similarly, a radar has a range within which it can effectively detect/track the target. Beyond that range, electromagnetic waves do not stop but carry on their travel for a long distance while getting attenuated in due course. So to detect the presence of a radar, a simple high-power radio receiver, very much synonymous to the common radio receiver, tuned to the radar frequency suffices. ESM systems have many radio receivers scanning over different frequencies. If these detect any signal, these stop scanning and fine tune to that particular frequency. Once it is done, direction of that signal can be found out and, further, the type of system that emits it can be detected.

How is it done? Each type of radar has www.efymag.com

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Fig. 13: Chaff shell firing (left) and animated evading (right)

During Doolittle Raid, epitomised by Hollywood movie Pearl Harbour, carriers and associated ships sneaked towards Japan under total radio silence. They had to do that to prevent the Japanese intercepting their communication and hence detecting their sneaking. In today’s scenario, radio silence will require all radio communications and radar emissions switched off, which is known as emission control (EMCON) state to operate in a certain frequency band to exploit the property of those frequencies. Say, for example, a radar that requires projecting a highly narrow beam with greater resolution requires an X-band frequency. So if the ESM module picks up a particular radar frequency, the type of radar operating could easily be found out.

The apparent strength of the signal indicates proximity of that radar.

Assume that the frequency used in the radar seeker of a cruise missile is found out. It is also found out that its strength is gradually increasing.

In this case, we can easily say that a cruise missile is on its way for a kill.

‘Know thy enemy’ is a rule in war. So every country tries to know all possible electronic signatures (nature of signals) of its enemy’s radar systems. Signals Intelligence (SIGINT) is a broad name for such operations. Nations do not hesitate to mount specific 007 kind of operations. All ESM systems maintain a library of known electronic signatures.

Just by comparing the incoming signature with the library, the ESM module can easily find out the kind of system that is operating.

ESM is not only limited to radars www.efymag.com

but is used for communications also.

Enemy communications will be intercepted by consistently sweep tuning to the entire frequency band. A radio voice communication detected indicates that there is enemy radio activity. The intelligence personnel embedded with the carrier strike group (CSG) decode and translate enemy communications.

The enemy also has ESM facility.

So if the CSG has to sneak near enemy shores, it has to maintain radio silence. In that case, the enemy ESM facilities serve the CSG to operate, like a blind man with acute ears.

Electronic counter measures.

Denying the enemy the advantage of electromagnetic waves is called an ECM. This includes two approaches, namely, hard kill or jamming, and soft kill or spoofing.

Hard kill/jamming. Jamming is synonymous to shouting loudly so that others cannot converse. If noise is injected in the telephone line, it naturally prevents a speaker from hearing what the other person is saying. Similarly, when a particular frequency has to be jammed, the ECM module generates and broadcasts a powerful signal in that freElectronics For You | November 2015

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DEFENCE quency. Known as noise jamming, this prevents the enemy radar from effectively executing its job.

There are many types of jamming that are carried out. Jamming techniques fall outside the purview of this article. Radio communications can also be effectively jammed apart from radar jamming.

Spoofing. This can be done electronically and also by other means.

That is, to make the enemy radar see a target where actually there is none and also to make the radar not see the target where it actually is.

Electronic spoofing methodologies fall out of the purview of this article.

Another effective means of spoofing is through chaff. Tiny, weightless metal foils like the husk of food grains are called chaff. Chaff is dumped in thousands in a shell and fired through mini cannons in the path of the radar of, say, an incoming missile. The shell explodes high up in the air and lets the chaff out. Length of the chaff is half the wavelength of the radar for better signal reflection.

Being very thin and light, these foils stay in the air like a cloud and take time to settle down. So in this intervening time, these effectively reflect radar energy.

Simultaneously, the ship rapidly changes its course. The distance and direction of the chaff shell firing is controlled by EW systems. By skilfully firing chaff in the path of the cruise missile, a carrier has a fair chance to mislead the cruise missile to fly away from its course.

Airborne EW systems. Apart from the built-in ESM and ECM systems, the CSG can employ EW aircraft called EA-18 Growlers. These aircraft have a variety of jamming systems and can fly to an area according to the requirement and jam the enemy radar and communication systems.

Typically, when combat aircraft are sent to strike ground targets deep inside enemy territory, the targets are heavily defended by surface-toair-missile (SAM) systems. It is these EW aircraft that first enter the area 68

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and perform jamming to protect the strike aircraft from SAM systems.

These aircraft are also capable of gathering signal intelligence by gathering enemy signal samples. Airborne EW systems also work in conjunction with ship-borne EW modules.

Under-sea warfare

emits Ping sounds and looks for echoes. Active sonars are complemented by passive sonars. Passive sonars only listen to underwater sound. Unbelievably, sound waves travel enormous distances due to convergence zones in oceans. These zones occur as concentric circles for every 61km from the source of sound.

Experienced passive sonar operators can detect even the sound resulting due to a sailor accidentally dropping a tool in the submarine.

When an enemy submarine is detected, the destroyer may engage it with torpedoes for close-range engagement and a missile-torpedo combo for long-range engagement.

The latter is a missile with a torpedo as a warhead. If the submarine’s presence is detected at a fairly longer range, this missile takes the torpedo near the target area where the torpedo jettisons itself and dives into the sea. From there the torpedo continues the attack.

Further, to increase the range of submarine detection, onboard undersea warfare helicopters called Sea

A threat for CSG is the presence of an enemy submarine. For a submarine, the prize target is the carrier of the CSG. Submarines use anti-ship cruise missiles for long-range engagement and torpedoes for close-range engagements. Modern-day nuclear submarines can submerge at their will for months together.

For a CSG, the first line of defence against submarines is formed by associated nuclear submarines. These submarines sail far ahead of the CSG and look for enemy submarines.

Ocean surfaces are not plain; there are gorges and canyons under the sea. Such oceanographic features are exploited by enemy submarines.

Submarines of the CSG look for the enemy submarines at these points.

If they find one, then and there it is engaged.

The second line of defence is formed by associated Aegis destroyers. These have both active and passive sonars mounted on their respective hulls. These sonars are called hull-mounted sonars.

An active sonar Fig. 14: EA-18 Growler

During the Falklands war between the UK and Argentina, British nuclear submarine HMS Conqueror launched three torpedoes and sank Argentine cruiser ARA General Belgrano. As an aftermath, Argentine carrier ARA Veinticinco de Mayo was sailed back to the harbour to protect it from the British submarine. In the 1971 IndiaPakistan War, the lone Indian carrier INS Vikrant had to be anchored near Andaman Islands to protect it from Pakistani submarine PNS Ghazi. INS Vikrant came to action only after PNS Ghazi was lured and destroyed outside Vizag harbour www.efymag.com

DEFENCE white paper. But, what happens when the enemy submarine is sailing underwater? There comes MAD. Magnetic anomaly detector. A submarine is a colossal mass of metal sailing underwater. Magnetic field disturbances are created by the metallic mass’s interaction with the water’s different temperature gradients.

MAD picks up these disturbances and detects submarine activity.

Then, it transmits the location of the submarine to the destroyer through datalinks.

MADs are only a part of the detection system. Whereas, to pin the exact location of the submarine, helicopter’s dunking sonar and dispensable sonobuoys come into play.

Dunking sonar. The helicopter hovers over the water surface and dunks sonar equipment. After dunking, resulting sonar readings are recorded and transmitted to the destroyer. This, the helicopter does at various locations in the sea. In the destroyer, readings from sonars are processed in underwater warfare command-and-control (C2) systems.

This system comes directly under Aegis C2 system of the destroyer.

Another method for detecting enemy submarine activity is through dispensable sonobuoys.

Dispensable sonobuoys. The helicopter strategically dispenses these sonobuoys at places where submarine activity is suspected or expected. These sonobuoys separate into two sections as sonar equipment Fig. 15: Hull-mounted sonar and as a buoy. Sonars emit ultrasonic sound pulses as beeps and receive echoes like whales.

Output of each beep is transmitted to the helicopter through buoys.

A sonar computer in the helicopter collects information from various sonobuoys and transmits data to the underwater warfare C2 centre Fig. 16: A torpedo being launched from an Aegis destroyer

Hawks are used by destroyers. More such helicopters are at times housed in the carriers also. These helicopters fly ahead of the CSG in a pattern and try to pin down the submarine.

These have special sensors such as forward-looking infrared (FLIR) imaging systems, magnetic anomaly detectors (MADs), dunking sonars and dispensable sonobuoys to detect submarines.

FLIR imaging system. This is a high-power night-vision device used to detect surfaced submarines even in pitch darkness. The system senses the heat emitted by the submarines and is useful only when the enemy submarine has surfaced to get fresh air. In an FLIR, the surfaced submarine will stand out like a black spot on a plain,

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DEFENCE

Fig. 17: Under-sea warfare helicopter

Fig. 18: A sailor loads dispensable sonobuoys in an under-sea helicopter (left); an under-sea warfare helicopter carrying a torpedo (right) and dispensable sonobuoys can be seen above it

of destroyer. This system creates a picture of the underwater scenario by comparing the received echoes.

Each sonobuoy receives an echo.

Depending upon their locations, the echo is received late or early.

Through a process called triangulation, exact location of the submarine can be pinned down. Not just one helicopter, but helicopters from other destroyers are pressed into service, depending upon the combat situation. Because once a submarine’s presence is detected, the CSG puts in every helicopter to detect and neutralise that submarine. A fairly clear underwater picture can be evolved by these destroyers.

If the submarine is detected within the range of a helicopter, the under-sea warfare C2 system from the destroyer sends launch commands for a helicopter to launch a helicopter-launched torpedo.

The carrier, which is the prize target for a submarine, ironically, has neither strike capability against submarines nor strong organic submarine-detection capability. It has to defend against the submarine only when the submarine passes through the perimeter created by destroyers.

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The only defence it has against enemy submarines is through a torpedo decoy to seduce away the torpedoes launched by enemy submarines.

Torpedoes sense the noises chug chugs and murmurs generated by the target’s propellers and engine, respectively. There are certain torpedoes that track the wake created by the ships. The torpedo decoy is towed behind the carrier at a long distance. This decoy has a sonar that only looks for the sound of an approaching torpedo. When it detects an approaching torpedo, it produces a sound mimicking the sound produced by the carrier’s propellers and engine murmurs. The sound is so powerful and realistic that the torpedo is clearly attracted towards the decoy instead of the ship and thus gets spoofed. Employment of this decoy is a worst-case scenario in which associating ships have got sunk by enemy action.

Surface warfare If a large flotilla of enemy surface ships is spotted faraway by E-2C airborne early warning (AEW) aircraft, F-18 combat aircraft carrying anti-ship missiles may be sent to fin-

ish these off. This is the long-range engagement but it is the destroyers that normally take care of mediumrange engagements. Aegis C2 system keeps detecting and tracking surface targets. This is done by AN/SPS-67 surface-search radar, AN/SPY-1 radar and AN/SPG-9 radar.

For medium-range engagements, anti-ship missiles called Harpoons are used. These missiles are capable of reaching 100km. For short-range engagements, 12.6cm (5-inch) guns, or, simply, guns, are used to engage in a classical way.

In short-range engagements, the range, bearing and speed of the target are continuously updated and transferred to the gun’s fire control system (FCS). The FCS plots the course of the enemy surface vessel. Then, it calculates the elevation and orientation of the gun to be maintained and actuates the gun, accordingly. It even takes wave motion into account. If the destroyer is heaved one metre up, the shell may land far away from the intended target. So the FCS stabilises the gun accordingly and maintains it in the required orientation.

At the command of the gunner, the FCS fires the gun. This gun can fire in rapid succession since the shells are loaded into the gun through an automatic loader. The destroyer has one such gun and the cruiser has two (one at the front and another at the back).

For medium-range engagements, Aegis system feeds the target coordinates to Harpoon anti-ship missile’s FCS. For targets beyond the radar horizon, the carrier-borne AEW aircraft or even satellites provide the target’s location. These transmit data to the carrier from where it is transferred to the Aegis C2 system and then to Harpoon’s FCS. Harpoon’s FCS derives the trajectory to be followed by the missile and programmes it into the navigation system of the missile. When fired, Harpoon being a fire-and-forget missile flies itself towards the target and destroys it. Initially, Harpoon uses its www.efymag.com

DEFENCE at high speed. Before anyone knew why it was approaching at such high speed, the boat rammed the ship and exploded. A huge hole was created on the hull and 17 US Navy personnel were killed, almost sinking the ship. Later invesFig. 19: The 12.6cm (5-inch) gun firing in a destroyer tigations and analyses showed that the blast was caused by Al Qaeda suicide terrorists.

After the attack on USS Cole, gravity of the emerging scenario was realised. These boats presented themselves as small-size fast-moving targets. Such targets are difficult to shoot down by the 12.6cm (5-inch) guns of Aegis Fig. 20: Harpoon missile firing from an Aegis cruiser ships. Moreover, technologies are already in navigation system to fly the trajectory place for remotely piloting such boats. entered into its guidance system by So dozens of such boats can simultaits FCS. Upon nearing the target, say, neously engage each escorting Aegis 40km, it uses its radar seeker and ship and damage it. Such attacks are called swarming attacks (like a group finds its intended target.

Tackling asymmetric threats. of honey bees attacking an animal). It The general perception of US Naval was realised that if such a swarming planners was that elements of a CSG boat attack is successful, Aegis escorts are slightly vulnerable to anti-ship will probably sink progressively, thus missiles. But sub-surface and sur- leaving the carrier vulnerable and on face threats were considered as well its own.

Such boats could only be shot covered due to CSG’s superior radar/ sonar and offensive capabilities. down by manually-fired light canThey expected that such long-, me- nons (type of heavy machine guns). dium- and close-range threats would Normal machine guns fire slugs, be neutralised by these capabilities whereas, these light cannons fire before these would indeed become explosive shells. But with both the ships and fast-moving target boats an actual threat.

But the art of war is not static; being heaved by waves, these mait is highly dynamic. New types of chine guns were not efficient.

When the ship heaves up/down, threats emerge at any point of time.

On October 12, 2000, an American the shooter has to tilt the gun downAegis destroyer called USS Cole wards/upwards to hit the target. It is felt the brunt of such a new threat. difficult to shoot a single target, but This new threat was suicide boats. it is practically impossible to shoot USS Cole docked in Aden harbour down a swarm of suicide boats. So for refuelling. After some time, a a sophisticated weapon system was small boat approached the destroyer needed, and that resulted in the www.efymag.com

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DEFENCE just a flick of a switch, can select from two different types of ammunition depending upon the combat situation.

The EOS also has a stabilisation circuitry.

This MGS is physically position-stabilised using motors, which are, in turn, directed by this stabilisation circuitry. This stabiliFig. 21: Mk-38 MGS with EO sight highlighted and operator station sation circuitry uses highlighted (inset) semiconductor accelerometers, which provide an output whenever their physical orientation is changed (due to waves). The stabilisation circuitry accordingly directs the motor and keeps the cannon stabilised. When the ship heaves up, this stabilisation helps to Fig. 22: TLAM being launched (inset); in-flight photo taken from a keep the gun to face chasing aircraft the point at which the development of MK-38 machine gun crosshairs of the EOS point. The computer present in the EOS checks orisystem (MK-38 MGS).

This weapon system, a computer- entation of the crosshairs of the EOS. There is a laser range finder controlled system, takes commands from the shooter sitting at a remote present in the EOS that detects the console, present somewhere deep distance of the target. The EOS cominside the ship. For this weapon puter automatically orients the gun, system, an electro-optical sight so that when fired, shells land at that point where the crosshairs are point(EOS) acts as the eye. This is a video camera that can see even in Stygian ing. The EOS computer maintains darkness. The EOS and the gun are the gun on the required orientation regardless of the ship’s heaving. situated on the same mount. Both the This system is expected to be gun and the EOS can be trained to an angle simultaneously, and also the capable of efficiently neutralising EOS can be trained separately. This is suicide boats even before these can approach the ships. It is being prodone through the remote console that contains a pair of joysticks, one each gressively fitted in the vessels of US Navy. for the EOS and the gun.

A 30.5cm (12-inch) colour LCD displays real-time imagery from the Strike warfare EOS. Various zoom levels are pos- Strike warfare, the only offensive sible to have a closer look at possible operation and purpose of the CSG, targets (suspicious boats). The EOS is neutralising land targets deep incomputer also generates crosshairs in side enemy territory. Targets can be the LCD screen. These crosshairs are airbases, marching troops, rolling used by the remote operator to aim at tank columns, bunkers, SAM sites, the target. The remote operator, with factories, power plants, dams and the 72

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like. For neutralising these, the CSG has two options; one is by launching combat aircraft and the other is by firing land-attack cruise missiles.

Tomahawk land attack missiles (TLAMs). When a requirement to strike a target arises, possibilities are assessed. If the target is a single target, say, a command bunker, situated deep inland, it will be well defended by enemy SAM systems all the way from the shoreline. A single-strike aircraft cannot be sent to engage the target situated deep inside enemy territory.

Enemy would also have combat aircraft nearby. The strike aircraft has to fight both the enemy combat aircraft and enemy SAM systems.

So a group of four strike aircraft is launched. These aircraft may need refuelling aircraft and EW aircraft like E/A-18 growler’s support. Even then if the threat level for the strike aircraft is high, TLAMs will come into play. These are complementary to strike aircraft. These are high-precision land-attack cruise missiles capable of hitting one building among other buildings. TLAMs have a range of more than 1000km and are nuclear-capable.

Aegis destroyers and cruisers are armed with TLAMs. The CSG commander issues target details through a strike-warfare commander to the ship that has to launch the missiles, which are fed to the FCS of the TLAM. TLAM’s FCS, in turn, feeds trajectory and target details to the missile’s guidance system.

Theoretically, a CSG can launch as many as 300 TLAMs in minutes but these do not carry that many. TLAMs typically start the strike by taking out enemy air-defence C2 centres.

This blunts the enemy’s air-defence architecture. Following these strikes, strike aircraft are launched to take out the targets assigned to these. This is how Operation Desert Storm was conducted against Iraq in the year 1990.

Air operations will be covered in the next part.

To be continued next month www.efymag.com

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Part 4 of 5

American Carrier Strike Groups: An Electronic Perspective

I

n the previous parts of this article, we discussed air defence warfare, electronic warfare, under-sea warfare, surface warfare and strike warfare. Let us take a look at air operations in this part.

B. Kamalanath is a technical writer. He is also a research scholar, pursuing Ph.D in military technology

Fig. 23: CATCC; the person sitting at the front is the approach controller

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Air operations Though air operations also fall under strike warfare, these are specialised operations of a carrier and, in turn, carrier strike group (CSG). Air operation from carriers is highly complex and highly dangerous. To support air operation, a myriad of electronic systems are installed in the carrier.

A combat aircraft is launched from the carrier through a system called catapult, which is driven by steam. Since aircraft on a carrier do not have sufficient distance to run and take off, the catapult proves very useful. An aircraft is placed on shuttle of the catapult and launched; aircraft is airborne in just two seconds. Steam pressure that has to be maintained is controlled through electronic systems much similar to industrial systems.

The catapult launches aircraft in air and

DECEMBER 2015 | ELECTRONICS FOR YOU

then the aircraft using its full engine power ascends to an altitude. After that, it leaves for its area of responsibility. Ensuing combat actions are out of purview of this article, however the return leg is covered here.

For retrieving and receiving an aircraft on the carrier, a plethora of electronic systems support the eventual landing on the carrier.

But before landing, aircraft must navigate towards the carrier.

Navigation In the sea, even gigantic carriers appear smaller than a dot for their aircraft flying at heights greater than 10km. At those heights, visually sighting the carrier becomes impossible. To retrieve the launched aircraft, the carrier must reveal its position to the incoming aircraft. The carrier does this through a system called TACtical Air Navigation (TACAN).

TACAN. Through a TACAN transponder the carrier continuously relays its identity in Morse code at a particular frequency.

Through appropriate antenna arrangement, it maintains a cardioid radiation pattern for this transmission. Aircraft can receive these signals by tuning their TACAN receivers.

These receivers compare aircraft’s bearing with the direction of the signal reception and give the bearing (direction) of the carrier to the pilot. The TACAN receiver also gives the slant range, known as crow-flight distance, of the carrier.

For this, aircraft’s TACAN receiver interrogates the carrier’s TACAN transponder with an interrogate pulse. The TACAN transponder receives that and, after a delay of 50μs, sends a reply signal. Aircraft’s TACAN receiver receives this reply. Then, by knowing the time at which the receiver had sent the interrogating pulse and the time it received the reply, it calculates the roundtrip distance time. This time minus the 50μs delay is the actual round-trip distance time.

With the speed of the radio waves known, WWW.EFYMAG.COM

DEFENCE range is calculated, which is the crow-flight distance.

Typically, a TACAN transponder of a carrier can provide navigational data to approximately 100 aircraft, simultaneously interrogating at a time. With TACAN, an aircraft can accurately navigate to the carrier.

Direction and range are displayed in the aircraft’s moving map display as waypoints and also as pointers in the pilot’s head-up display (HUD). (Refer ‘Fighter Aircrafts,’ article published in July 2007, August 2007 and September 2007 issues.)

The next task is to control the movements of outbound and inbound aircraft. Appropriate commands and support are given to inbound aircraft for landing. This is done by carrier air-traffic control, which is generally called amphibious air-traffic control.

Air-traffic control Since both the carrier and aircraft are moving, air-traffic control is much more complex and elaborate than their land based counterparts. All these operations are controlled from a command centre called carrier air-traffic control centre (CATCC).

This command centre is situated on the top-most storey, called Pri-fly, above the flight-deck of a carrier. All aviation-related data like aircraft’s flight plans and approaching aircraft’s status are assembled at this centre for air operations to be monitored and controlled.

For these control operations, many radar systems play a crucial role. Outbound aircraft are allotted a 3D air corridor through which these leave without interfering with incoming aircraft. Incoming aircraft from various locations are first marshalled to another air corridor and then assigned height, direction and speed to fly in a pattern around the CSG. Depending on the status of the aircraft—whether low on fuel or hit by enemy but in a flyable condition or having technical snag—these are assigned priorities. As incoming aircraft of high priority keep landWWW.EFYMAG.COM

Fig. 24: Antenna of AN/SPN-43 marshalling radar

ing, aircraft flying around the CSG are instructed to move to hold pattern around the carrier. As aircraft keep landing, a landing sequence is formed where aircraft trail behind each other by kilometres.

Once aircraft are lined for landing, these are transferred to approach and landing controllers, that help the pilots in landing the aircraft. During high-intensity air operations aircraft come and land every 30 seconds.

For this, a radar called marshalling radar is used, which is the air-traffic control radar.

Marshalling radar. The marshalling radar AN/SPN-43 is a 2D air-surveillance S-Band (2GHz-4GHz) radar, dedicated for air-traffic control. It is used for vectoring carrier-bound aircraft into final approach for landing.

It also acts as a back-up, short-range, air-search radar for air-defence operations. It provides azimuth and range of detected aircraft from 80.5km (50 miles) to a minimum range of 229m (250 yards), at altitudes from radar horizon to 9144m (30,000 feet).

The radar has an inbuilt Identify Friend or Foe (IFF) system. The radar display console displays all echoes in the area of responsibility in the form of blips. But how can individual aircraft be set apart from these blips?

For this, a system called Direct Altitude and Identity Readout (DAIR) is used to identify the aircraft.

DAIR. DAIR is a highly-automated beacon and radar-tracking system.

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DEFENCE ling and monitoring task dealing with outbound aircraft, incoming aircraft, landing aircraft, civilian and neutral flights, unidentified blips and the like.

Landing: the mortal challenge

Fig. 25: FA-18 combat aircraft on the carrier approaching land at dusk (centreline lights are visible and a tiny green spot on the left side is FLOLS)

Fig. 26: AN/SPN-41 radars highlighted (the top-left highlighted section is the LSO station)

It is used for identifying incoming aircraft and operates as a sort of back-end for marshalling operations, whereas the radar operates as the front-end. Every American combat aircraft has a transponder. This transponder is queried by DAIR through AN/SPN-43 radar.

These transponders give their identity and altitude of the aircraft to DAIR through AN/SPN-43 radar.

Then, DAIR superimposes this data as alphanumerals over the blips of corresponding aircraft appearing on display consoles. So mere anonymous blips are replaced by names and their altitudes. This system is also capable of processing and su60

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perimposing flight plans, geographic reference points and map lines for enhancing mission planning.

Marshalling radar-DAIR combo is a high-precision system enabling controllers to track every aircraft effectively. Through their consoles, air-traffic controllers can interact with DAIR for tracking a particular aircraft’s flight. Then they give instructions for the pilot through separate communication channels that exist between air-traffic controllers and pilots. They line up aircraft in a queue for landing and then transfer the control to the landing controllers.

In CATCC, there are many personnel, each handling a specific control-

For any pilot, landing his aircraft smoothly is a challenge. But normal pilots come nowhere near their naval counterparts. Naval pilots have to land their aircraft on a moving aircraft carrier, which is the supreme challenge comprising layers of challenges for a pilot’s airmanship because of the landing procedure. So naval pilots are considered a special breed among pilots.

Normally, an aircraft after landing runs over the runway, sheds off the enormous momentum, slows down and stops. But the flight-deck of a carrier is not even one-tenth the length of a runway. So the aircraft has to be arrested and trapped to stop its momentum. All aircraft belonging to carriers have a hook, known as a tail hook, beneath their tails. During landing, pilots touch the runway such that the hook snags a thick arresting cable present on the flight deck. The pilot has an error margin of just centimetres. If missed, the pilot increases power, takes off and makes another attempt.

Now comes the next aspect of the challenge—the runway is not only short but also unstable. It pitches up/ down and rolls left/right. The pilot has to land guessing how the runway will move and then land, accordingly.

The pilot has to guess that in just fractions of a second. During landing, the pilot first aligns the aircraft to the centreline of the runway from an altitude and gradually descends at a constant speed in a shallow angle; it is called approach. In the meantime, if the flight-deck pitches up, the pilot nudges the throttle to increase speed and hence altitude, and vice-versa.

Similarly, if the carrier yaws, the pilot adjusts the aircraft, accordingly, and may have to make more than 100 such adjustments during the approach.

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DEFENCE Further, landing at night time on a very short runway of a minimallylit carrier, which is pitching, rolling, yawing and sliding, is nerve shattering and a mortal challenge.

An error caused due to the pilot’s judgement may cost not only his or her life but many other lives and also many aircraft.

Previous generations of pilots had only two optical clues to align the aircraft with respect to the carrier and then land safely. The first was called Fresnel Lens Optical Landing System (FLOLS) for vertical positioning of the aircraft. The second was called Centreline Lights for horizontal positioning of the aircraft. But modern-day pilots have an electronic aid called Precision Approach Landing System (PALS).

Precision Approach Landing System PALS is really a pal for naval pilots.

It has three modes: instrumented carrier landing system (ICLS) mode, automatic carrier landing system (ACLS) mode and talk-down mode.

ICLS mode. For an aircraft to land, it has to maintain a constant recommended speed, while losing altitude gradually, until touchdown on the runway. How it loses altitude with respect to the runway is called glideslope. For a runway on ground, the glideslope never changes but since the carrier rocks up and down, the glideslope also varies accordingly and is never constant. So a mere pitch up of the flight deck is drastic for the landing aircraft. Pilot of the aircraft must be made aware of this changing glideslope. This is done through a system called ICLS centred on a radar system called AN/SPN-41.

Though technically not an exact radar system, AN/SPN-41 engages in one-way transmission to the landing aircraft in Ku-band. It has a set of radars: a centreline unit and a flight deck unit. The former is situated beneath the centreline of the runway and the latter is situated slightly high on the flight-deck.

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Using sector scanning, both units acquire and track the approaching aircraft. The fightdeck unit and centreline unit respectively measure the aircraft’s vertical and horizontal deviation from the glideslope. Then AN/SPN-41 broadcasts the positional difference in pulse mode in Ku-band in real-time.

A system called aircraft approach control system (ACCS) present in the aircraft receives these signals. It extracts the positional information of the aircraft with respect to the glideslope from these signals. It then converts these signals as a set of horizontal and vertical lines on the pilot’s HUD. The vertical line indicates the position of the aircraft with respect to the centreline of the runway. It appears in the direction that the aircraft has to move so as to align with the centreline of the runway. The horizontal line indicates how much the aircraft must gain or lose altitude to fit in the glideslope.

When these two lines form a crosshair, the aircraft can be perfectly aligned with the glideslope.

The pilot, after aligning with the glideslope, can gently nudge his controls to stay in the pitching glideslope until touchdown.

Talk-down mode. In this mode, the pilot is instructed by landing signal officers (LSOs). They work from an LSO console situated at the edge of the flight deck. This console gathers all flight data of the approaching aircraft from many systems. The LSO console computes the required flight path for landing, monitors the flight path of aircraft and the difference that the pilot has to cover. It takes inputs from the integrated launch and recovery television system (ILARTS), AN/SPN-44 radar and wind-measurement system.

ILARTS. This is a camera-andtelevision system with all-weather capability. In simple words, its cameras can videograph both during day and night with equal clarity. ILARTS has remotely-operated cameras at many ELECTRONICS FOR YOU | DECEMBER 2015

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Fig. 27: Two frames of ILARTS imagery (left) (Image courtesy: wikipedia); the dash near the left side scale is the position of the aircraft with respect to glideslope. ILARTS control centre (right) (Image courtesy: US Navy)

Fig. 28: LSOs and LSO console showing an approaching F-18 aircraft (highlighted)

places on the flight-deck. These cameras videograph the approaching aircraft along with its relative position with the horizon. ILARTS then adds glideslope crosshairs parameters and other data to that imagery. The resultant composite video is displayed at the LSO console, CATCC and other important centres like CDC. The aircraft’s alignment with respect to the horizon indicates the LSO whether the aircraft should climb up or descend so as to capture the glideslope of the pitching flight deck.

Fig. 27 indicates the two scenarios of an aircraft approaching for landing. The scale-like symbol on the left indicates acceptable limits for the aircraft in the vertical axis. The dash symbol near this scale indicates the position of the aircraft. The aircraft has to be ideally at the centre of the crosshairs. The dash indicates the actual position of the aircraft with respect to the glideslope. If the 62

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aircraft is not within this envelope, it is waved off for another approach.

These symbols are generated by ILARTS and fed to the LSO console.

AN/SPN-44. This is known as a range-rate radar. It detects approaching aircraft, tracks it and calculates its speed (both relative to the carrier and true speed). It then provides this data to the LSO console. Supplied with this accurate information on the speed of the approaching aircraft, LSOs can wave off the aircraft attempting to land at an unsafe speed.

Wind-measurement system. This is nothing but a traditional windmeasuring system based on an anemometer. It is used to measure headwind, tailwind and crosswind speeds. These winds can terribly affect the aircraft’s flight by shifting the aircraft. Headwinds resist flight, tailwinds push the aircraft forward and crosswinds laterally move the aircraft out of glideslope. These winds are

troublesome. Data from the system is fed to the LSOs, who, in turn, intimate the same to the pilot. The pilot then flies in a way offsetting the effect of these winds.

Based on these inputs, LSOs communicate with the approaching pilot, who constantly adjusts aircraft’s position based on the voice commands given by LSOs. ACLS mode. Imagine that a pilot is returning to the carrier from a battlefield, which is located 500km away, after bombing enemy targets and evading enemy air defence missiles. On the way back, he or she had to intensely fight with enemy fighter aircraft. Now, on returning to the carrier, the pilot has to land his aircraft under pitch-black conditions. The pilot’s physical state is not as alert as it was when he or she left for the mission; the intense adrenalin rush has tired the pilot, making landing of the aircraft even more difficult. Anyone in this situation would dream of a system that lands the aircraft automatically without any inputs. ACLS is that dream system.

Parts of this system exist in both the carrier and the aircraft.

Only ACLS-equipped aircraft can be landed automatically on a carrier.

Basically, in an ACLS, autopilot of the aircraft is controlled by the carrier. For this, position of the aircraft is tracked through Ka-band tracking radar AN/SPN-46 in the carrier. Instructions for the autopilot are transmitted to the aircraft. There are two radars guiding each aircraft.

The sequence starts from a point called acquisition window during approach of the aircraft. At this point, the tracking radar acquires the aircraft and starts tracking it. At this point the pilot is indicated through cockpit indicators that the aircraft is being acquired by ACLS. The pilot then puts the aircraft under autopilot in landing mode. The tracking radar uses a conical scan antenna and continuously interrogates a radar beacon present in the aircraft. This WWW.EFYMAG.COM

DEFENCE

Fig. 29: AN/SPN-46 radar antennae

beacon responds in X-band for interrogation of the tracking radar. Replies of the beacon are continuously plotted on the ACLS computer to derive the aircraft’s location with respect to the glideslope.

Instructions to the autopilot are transmitted in real-time through a UHF datalink. Autopilot has a component called approach power compensator (APC), which increases or decreases the engine’s power to vary the altitude according to the glideslope requirement. The pilot has warning lights that give indications to abort landing and try for another attempt. Similarly, at any point of time, the pilot can disengage from autopilot by applying pressure on the control stick to take control of the aircraft.

The irony is that pilots do not use this mode! They say that they do not want a computer to land their aircraft. They instead use the instrumented mode and talk-down mode. So this mode only serves as a fallback option during haze and fog.

Mission planning systems Air operations are planned taking a large number of inputs from various departments and workspaces of the carrier. The following systems help in that planning.

Aviation data management and WWW.EFYMAG.COM

control system (ADMACS). This is a tactical, real-time LAN used for an aviation-related information-management system. This system helps to manage the aircraft’s launch and recovery operations. This network, extending to aviation-related spaces of the carrier, facilitates strike operation planners with necessary details about aircraft availability and aircraft under maintenance and repair, among others.

Aviation weapons information management systems (AWIMS).

This is a data management system to collect, distribute and display information used to manage weapons inventory in a carrier.

Integrated shipboard information system (ISIS). It is a data processing and display system. It integrates all crucial information like tactical, navigational, air operations and meteorological-related data and displays these in a single usable format. To the captain of the ship, entire data regarding the carrier is displayed. Down the hierarchy, only data relevant to a particular function is displayed at various work centres.

In the fifth and concluding part we will discuss command and control operations as well as cruise control operations.

To be concluded next month ELECTRONICS FOR YOU | DECEMBER 2015

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defence Part 5 of 5

AmericAn cArrier Strike GroupS: An Electronic Perspective

I

n the last four parts of this article we covered air defence warfare, electronic warfare (EW), under-sea warfare, strike warfare and air operations. In this concluding part, let us take a look at command and control (C2) operations as well as cruise control operations.

B. Kamalanath is a technical writer. He is also a research scholar, pursuing Ph.D in military technology

Radars—A revisit All surveillance and navigation radars are situated high up in the mast. In the age of sail ships, observers used to sit high up in the mast. Who can forget the observers ringing the bell after seeing the iceberg in the movie Titanic? Radars sitting high up in the masts give a greater radar horizon. Radar horizon is the maximum range at which radar can detect a target against the curvature of earth.

But presence of so many communication and detection equipment in the mast in interference. This requires

certain systems to be turned off when another system is working. If the turned-off system is an important system, and if the enemy knowingly or by chance chooses to attack during this window, the result can be catastrophic.

C2 operations Whatever may be the strength of force, it is only the right commands given at right times can make the force lethal. The commander who commands the carrier strike group (CSG) must know what is happening around him, the strengths and the weaknesses of the group.

For example, what will happen if the commander issues a command to launch a surface-to-air missile (SAM) when stocks of SAM have been exhausted? He must know the threats and his capabilities, and must be present in the carrier to command the CSG. For effective command, the commander requires an efficient C2 system.

Backbone of C2 systems is the communication systems that include voice links and datalinks.

Communication systems

Fig. 30: Radars in the mast of the carrier. The reader may try to identify the radars present in the masts of the carrier. This image covers many radars and also an ECM module (Image courtesy: US Navy) WWW.EFYMAG.COM

The mast of the carrier is littered with numerous antennae—protected by radomes—for various communication systems and datalinks present in the CSG. Almost all sorts of antenna systems are seen in the carrier right from whip antennae situated in the flight deck to wire-fed fan antennae present above the superstructure. A plethora of communication systems operating at various frequencies and following various techniques of transmission could be found in the CSG. Terrestrial radio communication. It has both military and non-military radio communication facilities operating in MF, HF, VHF and UHF bands. Military communications are secured through encryption ELECTRONICS FOR YOU | JANUARY 2016

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defence and are used to communicate with CSG members. Even if the enemy intercepts military communication, they will not be able to understand the message.

VHF is used for ship-to-ship or helicopter-to-ship communications. Military HF and MF have a range of around 300km. VHF and UHF, due to their high-frequencyinduced attenuation, have a range of around 100km.

Non-military radio communication is not secure. It is used to communicate with harbours, ships and aircraft of civilian or neutral origin. Non-military UHF systems can be used up to a range of 50km; all other band systems have the same range as that of their military counterparts.

Satellite communication systems. Aircraft carrier, being the commanding ship of the CSG, has a variety of dedicated satellite communication systems for various purposes. Long-distance communications are carried out through the USA’s defence satellite communications system (DSCS), a dedicated satellite based communication network. This high-capacity global system uses SHF band geostationary communication satellites that orbit equidistantly around the world.

On the other hand, short-distance communications are managed by fleet satellite communication (FLTSATCOM). Typically, this type of communication is between two CSGs or intra CSG communication or shore-to-CSG communication.

Satellite communication is carried out in two modes: receipt and broadcast. Receipt mode requires the recipient to send an acknowledgement message for each message it receives. Whereas, broadcast method, also called donot-answer mode, does not require an acknowledgement message.

In the latter mode, the CSG can 76

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keep on receiving the data that are sent to it. The great advantage is that the CSG can preserve radio silence. Because, the moment it sends an acknowledgement message, the enemy electronic support measure (ESM) systems can find the CSG’s location. Through this mode, the CSG can receive situational updates without revealing its position.

Tactical digital information links (TADIL) These tactical datalinks are the bridge between C2 systems of individual ships. Through these datalinks, Aegis ships exchange data between them and also with the carrier, so that overall C2 is maintained.

HMS Sheffield—a destroyer of the UK—was sunk during Falklands War by Argentine aircraft launching French-made Exocet anti-ship missiles.

It is said that at the time of attack, the ESM module of the EW system was not on due to interference problems with satellite radios. Had the ESM been on, perhaps, that ship could have survived the attack Link-4A. When airborne early warning (AEW) aircraft detect incoming enemy bomber, F-18 aircraft on patrol are instructed to fly towards the general area of the incoming enemy bomber. On reaching the area, these are vectored (giving directional commands) to intercept the bomber.

These are vectored through a datalink. The aircraft computer display in the pilot’s head-up display

(HUD) shows the waypoints to be followed to intercept the bomber.

Link-4A is one such data link. It is a non-secured two-way datalink used for providing vector commands to combat aircraft. It operates in UHF band at a data rate of 5kbps. It follows timedivision techniques. Also, aircraft are communicated during the following processes: automatic carrier landing system (ACLS), air traffic control (ATC) and during combat strikes.

Generally, Link-4A’s transmissions are not secure and could be jammed by enemy ECM. On the positive side, it is considered easier to operate and maintain.

Because of these reasons, this very old datalink is still being used by the US Navy. In a carrier, there are ten channels for this link and the typical range is as far as 500km.

Link-11. Link-11 is a halfduplex high-speed encrypted datalink. It operates in HF and UHF bands. It facilitates computerto-computer digital data communication between aircraft and ships.

Even if the signals are intercepted by the enemy, these cannot be understood by them because of the encryption. Data can only be decoded at the receiving terminal.

Positional information of the transmitter is also sent along the data so that the receiver can know the sender’s position. This feature is an important aspect of combat communication. Typically, data sent by a ship to the aircraft is received by appropriate receivers in the aircraft. There, these are decoded by decoders and sent to the aircraft computer.

Then, information is displayed to the pilot in a format that he or she can understand. Data can be anything like waypoints that have to be followed for reaching the new destination or positional data of the enemy combat aircraft.

Combat aircraft have an WWW.EFYMAG.COM

Missiles (TLAMs). electronic system called moving Sonobuoy datalink. This datamap display, which displays the link connects sonobuoys with the map of the terrain over which the under-sea warfare system present in pilot flies. As the pilot flies ahead, destroyers. These dispensable sonothe map also scrolls up accordbuoys are dropped by the submarine ingly. Waypoints are updated in the hunting helicopters in the areas display through this datalink. In the suspected with enemy submarine carrier, there are 62 Link-11 datalink activity. The under-sea warfare syschannels available. Each datalink tem deduces the submarine scenario is capable of communicating as through these datalinks. far as 300km.

Link-16. Link-16 is a node-less, C2 systems jam-resistant, high-speed, encrypted digital datalink. It operates in In a carrier, the storey above the 960MHz-1215MHz band. Based on flight-deck is called flag bridge.

TDMA technique, it is used by airCommander of the CSG controls all craft, ships and even ground forces operations from a command centre to exchange their tactical pictures in called tactical flag command centre near-real-time.

Typically, commanders of the CSG at sea can even get tactical pictures around ground forces operating deep inside enemy territory.

Link-16 supports exchange of text messages, imagery data and provides two channels for digital voice communications with a data rate of 2.4kbps and/or 16kbps in any combination.

The range is around 500km and there are 255 Link-16 datalink channels available Fig. 31: A GCCS-M display (Image courtesy: US Navy) in the carrier.

Officer-in-tactical command (TFCC), situated in this bridge. In information exchange sub-system naval parlance, flag indicates some(OTCIXS). This is a two-way UHF thing related to the commander satcom based datalink system for inof a fleet. tra- and inter-CSG communication.

Commander of the CSG gets This link supports the exchange instructions from his high comof targeting information for multimand through a satellite based C2 targeting of sub-surface, surface and system called global command and aerial targets. A ship can get radar control systems-maritime (GCCS-M). track data from other ships through Through this system, commander of this link even while not using its the CSG provides situation reports to radar at all. This is called over-thehis high command. horizon (OTH) targeting.

A system called advanced Tactical data information combat direction system (ACDS) exchange sub-system (TADIXS) creates the tactical picture around downlink. This is a shore-to-ship the CSG. Display of the ACDS gives one-way satellite datalink for the the CSG commander the tactical ships to receive mission plans for picture around the CSG for taklaunching Tomahawk Land Attack ing combat decisions.

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Similarly, captain of the carrier has another parallel ACDS display at his command centre called combat direction centre (CDS) from where he or she gets the tactical picture around the carrier.

Global C2 systems-maritime (GCCS-M). GCCS-M is a system that receives, processes, displays and manages data on the readiness of neutral, friendly and hostile forces in near-real-time. It does this via external communication channels, local area networks and direct interfaces with other systems. Any information the CSG commander required for the mission, be it intelligence or meteorological data, is sent through this system from the higher ups. It is through this GCCS-M system that the commander of the CSG takes orders from the higher command and passes situation reports to the higher command.

For a CSG commander, GCCS-M aids in the decisionmaking process by displaying relevant tactical information. For example, the CSG is anchored 300km from enemy shore. Job of the CSG is to neutralise an enemy nuclear missile base situated 200km inland. The condition for neutralisation is that the missile base readies itself for a nuclear missile launch.

But, how will the CSG commander know that the nuclear missile base is ready for missile launch?

This information can only be gathered by people of the likes of a man drinking a Vodka Martini and who is addressed as 007. Purely, the data he collects is intelligence related. Such information is not available through the CSG’s resources for the CSG commander. So in this case, intelligence has to be supplied by the high command to the CSG commander.

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Fig. 32: ACDS display (Image courtesy: US Navy)

CSG commander is issued an order to neutralise that base. This is done through GCCS-M. For such information exchanges, datalinks TADIXS and OTCIXS play a vital role.

The CSG commander can also access information through special wireless Internet systems. CSG is a node in secure internet protocol router network (SIPRNET), nonsecure internet protocol router network (NIPRNET) and joint worldwide intelligence communication system (JWICS).

SIPRNET is a military Internet system owned by Department of Defence (DoD) of the USA. It has only restricted access. Through this Internet, classified information is passed through packet switching.

NIPRNET is a type of Internet that is used to exchange sensitive but non-secret information between privileged users and at the same time provides them Internet access.

Again, Internet Protocol routers are owned by DoD of the USA. JWICS is DoD’s, top-secret version of the Internet, together with its secret counterpart, SIPRNET. Previously, GCCS-M was implemented through high-performance UNIX workstations because of their capability to run GCCS-M specific software. The trend of availability of increasing computing power and increasing software versatility is leading to a migration of GCCS-M towards off-the-shelf systems.

ACDS. This is a centralised, 78

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automated C2 system. It is used to collect and correlate combat information on the air, in the surface, sub-surface and EW environments. It acts as a central repository of all tactically significant targets (detected by radars and sonars) for the CSG. ACDS is a comprehensive system and contains many computers, a display system with many consoles. It integrates on a mainframe computer the information from carrier’s sensor systems, datalinks, navigation/air traffic control systems and weapon systems. This system is operated by 23 crew members.

Computers running applicationspecific software collate and correlate data. All surface and air search radar tracks and sonar tracks are communicated to the ACDS by Aegis ships of the CSG through datalinks. The respective ships derive their coordinates from their navigation systems called inertial navigation system, cross referred by a GPS. This they send with their identification data while sending track data. ACDS, after receiving all data, correlates it with various similar tracks and positional coordinates of that ship. For example, two ships present in the CSG but sailing at different locations might have sent track data of the same enemy aircraft to the ACDS. In reality, these tracks are nothing but the track of the same aircraft taken from different locations.

ACDS, after correlation, classifies that track as the same aircraft by comparing the positional coordinates sent by the ships. This is called grid-locking. Like this, the ACDS displays the tracks accord-

ingly to provide an overall tactical picture around the CSG. This gives the CSG commander the capability to identify targets, classify these and prioritize threats for easy decision making.

Based upon the threat, the commander initiates engagements like vectoring combat aircraft to targets, or launching SAM from a destroyer, or launching anti-ship missile from a destroyer.

Generally, all constituent ships of the CSGs are delegated with responsibilities to deal with threats occurring in their sectors. In one Aegis cruiser, the air defence command centre of the CSG, there is an air defence warfare commander working full-time. His or her commands are executed by the captains of Aegis cruisers and destroyers.

Similarly, there are commanders for underwater warfare, surface warfare, EW and strike warfare. The CSG commander can also exchange targeting information and engagement orders, not only within his or her CSG but also with other CSGs.

Cruise-control operations Cruise-control operations involve navigation and propulsion operations, and are carried out in a similar way as commercial shipping navigation.

Navigation. Navigation was done through compass in the olden days; then emerged sextants and printed navigation charts. These printed navigation charts are like a detailed map but for sea routes, and indicate depth of a certain area in the sea, width of straits and other information. Now, these charts are the tools of the past and are only used as a fallback option today.

Their roles have been taken over by a system called electronic chart display and information system (ECDIS), which takes inputs from electronic navigation charts (ENCs) and displays the area of interest.

These ENCs have complete WWW.EFYMAG.COM

propeller shafts.

Electronic systems that are used in controlling the nuclear chain reaction and associated functions of normal reactors are also found in the carriers.

These reactors can work continuously for 20 years without requiring Fig. 34: A helmsman on the bridge of a carrier (Image courtesy: US Navy) any refuelling.

With the aid of these reactors, carriers can reach Generally, the required instrucspeeds of 55kmph with ease. In nations for navigation are given by the val parlance, sailing at this speed is captain from the combat direction like driving a Formula One car, and centre (CDC). Necessary informaalmost 100 thousand tonnes of mass tion like a copy of navigation radar sailing at this speed is something displays is available at the bridge, unimaginable. which is the command centre for Other vessels of the CSG are not sailing the carrier. This bridge is the nuclear powered but are powered by first storey above the flight deck. diesel-fuelled gas turbine engines.

From here, sailors called helmsmen, Controls of these propulsion systems control the sailing operations. Aegis also resemble industrial-class deescorts also have similar navigation signs with military standard. radars and helmsmen controls.

Propulsion. A carrier’s propulRussian carriers: The other sion power comes from the electricside of the coin ity generated from two scaled-down nuclear reactors. These produce a Definitely, American CSGs are a shaft horsepower of 140MW to drive force to reckon with. But one cannot forget Prince Hector or Karna while speaking about Achilles and Arjuna, respectively. So, such a detailed literature on American carriers will not be complete without mentioning the Russian carrier force.

Traditionally, Soviet Navy’s and later Russian Navy’s speciality is that these are a submarine dominant forces. Though there are very much capable surface vessels in their navies, dominance of their submarines is greater. As water is the best antidote for fire, submarines are a perfect match capable of standing toe to toe with the CSG. But it did not restrict Soviet Union to try its part on carriers.

Basically, pioneers in naval technology are Britons. British Empire Fig. 33: Screen behind the woman sailor is ECDIS (Image courtesy: US Navy)

hydro-graphical information like navigational hazards, depth of a particular place, width of the navigable channel and a lot more, as electronic data.

GPS is used to find out the precise position of the carrier and other ships. This positional information is fed to the ECDIS, which displays all relevant data so that the navigator gets the complete idea of his or her position and surroundings.

Radar AN/SPN-67, which is also used in a ship self-defence system (SSDS) is used for navigation. Along with this radar, a radar called AN/ SPS-64 is also used for navigation. This radar operates on a fixed frequency of 9GHz and has a peak power output of 20kW. Its antenna can rotate at speeds up to 33rpm, which provides a high degree of target resolution and also allows target information update for every two seconds.

After detecting contacts through this radar, a system called automatic identification system (AIS) helps in identifying the nature of the contact.

AIS is a system that all sea-going non-military vessels must possess.

It relays its identification in radio frequency (like identify friend or foe, or IFF).

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defence sustained with the strength of their navy. World’s first carrier, HMS Argus, was a British ship. Many of the novel naval innovations are theirs, such as radars and sonars.

After the 1970s, the UK restricted itself to small carriers with aircraft, known as Harrier, capable to take off vertically.

Britons installed a ramp called ski jump at the edge of the carrier.

Harriers run through this ramp to get air-borne. Indian Navy is also operating such a carrier called INS Viraat and a handful of Harriers.

Strangely, Russians clubbed American and British practices.

Russian aircraft take off by running through the ski-jump like British, and land by tail-hooking arrestor wires like Americans. But Russian carriers are not meant for strike operations. Their purpose is to protect Russian nuclear submarines that carry nuclear warheaded intercontinental ballistic missiles (ICBMs) from the American long-range antisubmarine aircraft.

Russian carriers are designed entirely to operate alone unlike American carriers. The present Russian carrier Admiral Kuznetsov has the features of an entire CSG, but is scaled down. The carrier has a dozen or so fighter aircraft, sonars, early-warning helicopters and even phased array radars like American Aegis ones. There are also anti-ship cruise missiles (also with landattack capability) to hit targets at a range of more than 500km.

It is the most-protected carrier in the world. There are eight AK-630 close in weapon systems (CIWSs).

There are 192 3K95 Kinzhal readyto-be-fired SAMs of 15km range and capable of being launched every three seconds.

Apart from this, there are eight Kashtan CIWS-SAM combos. One combo contains two guns and 32 ready-to-be-fired 3K87 Kortik SAMs. So in total there are 24 CIWS and 192+256 SAMs. 80

JANUARY 2016 | ELECTRONICS FOR YOU

Fig. 35: INS Vikramaditya, the Indian aircraft carrier (Image courtesy: Indian Navy)

Who can forget the climax aerobatic stunts of Arnold Schwarzenegger flying an aircraft like a helicopter in the Hollywood movie True Lies? That aircraft is the US version of The Harrier Literally, these systems form a defensive bubble around the carrier against cruise missiles and also aircraft. A Soviet-era carrier called Admiral Gorshkhov even had an automatic landing system to guide their now-retired Yakolev-41 aircraft, Soviet’s answer to British Harriers.

This very same carrier has entered the Indian Navy as INS Vikramaditya and will serve the Indian Navy in the years to come.

The carrier was intensively modified and refurbished for the Indian Navy.

Now, it has become almost 80 per cent new. It also has an automatic landing system and will be getting a capable air defence system.

The CSG so far has been think-

ing about ways to tackle cruise missiles. But the Chinese development of a ballistic missile called DF-21D has changed the basics itself. This missile is said to have been developed to specifically target US Navy’s CSGs. This ballistic missile will reenter the atmosphere after its post launch flight through space.

Until this point, there is no difference between this missile and other ballistic missiles. But this DF-21D—after re-entry—will open its target seeker and look for the carrier. The enormous size of the carrier’s fight deck will be spotted by the seeker. The missile will then descent towards the carrier at a speed of 5-mach to 6-mach. At such speeds intercepting it will be very difficult. In the years to come, it will be interesting to see what the Americans are going to do to counter this missile.

In short, it is an eternal duel between Aircraft carriers and the means to counter aircraft carriers.

As long as the carriers remain in the scene, this duel will be on. As long as this duel goes on, both sides will use intelligent electronic systems as their weapons.

CONCLUDED! WWW.EFYMAG.COM