Hunters: The Evolution of the Antisubmarine Warfare Helicopter Beginnings of Antisubmarine Warfare

By LT Lauren "Bender" Chavis, USN

On a chilly October night in 1776, a watchman aboard a British frigate braces against the cold. The ship is anchored just off Manhattan and is tasked to maintain the blockade of New York Harbor. The half-moon lights the rolling swells, but not well. The watch stander squints against the night breeze and spots something. He thinks. Trash maybe. But it drifts against the current. Strange. It is too small to be a shipping vessel. Maybe a trick of the light. He blinks. It continues closing the frigate. He shouts a challenge. Nothing heard. He shouts again. Nothing heard. He turns, just for a second, to see if anyone else is witnessing this event. He turns back and sees nothing. Must have been a trick of the light.

Sergeant Ezra Lee sits scrunched in the Turtle, submerged just beneath the waves. He is piloting the clumsy vessel back to dock. That was a close one.

Unbeknownst to the watchman, he witnessed the first subsurface vessel utilized in combat: the Turtle, an American submersible that attempted to affix explosive charges to the underside of British ships in New York Harbor during the American Revolutionary War. Although its attacks were ultimately unsuccessful, the endeavor originated the concept of undersea warfare that grew to include the German U-boats of the World Wars, the ballistic missile submarines of the Cold War, and the modern submarines of today that are used for reconnaissance, deterrence, and offensive attacks.

As the watchman spotted and deterred the vessel, he also unknowingly spawned the field of Antisubmarine Warfare (ASW). Prior to the First World War, the primitive nature of submarine designs and their limited operational use meant ASW amounted to little more than acknowledging the existence of submarines. When they were employed, however, submarines held a distinct advantage over the surface vessels they faced, as they were difficult to detect, track, and attack. Spotting them was lucky. If they failed to slip away after detection, ASW attacks were limited to attempting to damage their periscopes with hammers or catch them in a net. However, as more capable submarines developed into World War I, so did efforts to combat them.

Antisubmarine Warfare during the World Wars

It is March of 1916. The German U-boat U-68 departs through the Ems River on her first war patrol, assigned to an operating area off the coast of Britain. She comes across an unflagged merchant vessel. She is unarmed, easy prey for the boat’s young captain, eager to make a name for himself with a successful engagement. U-68 positions herself off the merchant vessel’s bow and fires a torpedo. Miss. The U-boat surfaces, calculates another shot, and fires again across the ship’s bow. The merchant stops and launches a boat, a sign of surrender. The U-68 captain maneuvers his submarine to position alongside his captured quarry.

As the U-boat approaches, the vessel raises the White Ensign, a flag worn by British Royal Navy ships. This is no merchant. It is the Q-ship HMS Farnborough, a decoy. The Farnborough uncovers her guns and opens fire, striking U-68 several times. As the boat begins to sink, Farnborough steers to her location and deploys a depth charge, destroying the remains of the vessel. It is the first successful ASW weapons engagement on an enemy submarine.

During WWI, submarines became a major issue for surface vessels. Towards the beginning of the war, ASW relied heavily on visual detection of the submarine, and attack required warships to get in close to ram it or shoot it with guns. The invention of “indicator loops,” long cables meant to detect the magnetic field of passing submarines, and the advancement of mines, depth charges, and torpedoes eventually put a dent in the German U-boat inventory. For the first time, aircraft were also utilized to detect and sometimes destroy enemy submarines. While seaplanes and airships made successful attacks, their main role was deterrence—forcing U-boats to submerge, effectively preventing attack and navigation.

In the Second World War, while every major Navy had a submarine fleet, few had developed advanced tactics on how to combat them. After reinvigorating their submarine fleet in the interwar period, Germany wreaked havoc on Allied convoys utilizing “wolfpack” tactics and coordinated attacks of multiple U-boats over radio. In response, Allied ASW tactics and technology improved to combat the threat. Recognizing the advantage of aircraft in ASW, many technological developments focused on increasing airborne ASW lethality. The new technology included advancements in radio frequency detection capabilities, improvements in airborne radars, the development of airborne magnetic anomaly detection, and advent of sonobuoys, expendable hydrophones that detect and relay submarine acoustic information.

These technological advancements, in addition to improvements in Allied ASW tactics, neutralized the majority of the German U-boat threat and ultimately led to the Allied victory in the Atlantic.

Helicopter Antisubmarine Warfare

It is an early April morning in 1945, now a year since helicopters first flew in combat. A crew of young Navy and Coast Guard lieutenants and research scientists are not in combat, but they are in danger. They are the first flight test of a new technology, a helicopter-borne dipping sonar. The sonar reels out of the hovering helicopter into the ocean and listens for acoustics that operators can interpret to find and track a submarine. But the hover must be perfect to keep the cable directly underneath the aircraft, which is difficult with the primitive controls in the experimental helicopter with the unwieldy new sonar.

To aid the pilot in his precise hover, the crew tosses references in the water. Floating lights? Washed away. Dye markers? Blown by the rotor wash. The comic section pulled from a Sunday newspaper? Just right. The pages soaked in water, keeping them in place under the downwash, and the brightly-colored comics stood out in sharp contrast to the ocean water. A good enough reference for now. They’ll fix that later.

During World War II, Igor Sikorsky and his team of engineers demonstrated the R-4, the first helicopter adopted by the United States military. Although intended as a personnel recovery platform, it also proved helicopters could be practical for ASW patrol, extending the range of ship sensors. Of particular interest was the possibility of an airborne dipping sonar that could be deployed from a helicopter, listen for submarine acoustic signatures, be recovered, and re-deployed to continuously track a submarine.

The United States Naval Research Laboratory designed an underwater sound recorder and, starting in 1945, installed it first on an experimental helicopter, then on the more powerful Sikorsky H-5, and ultimately on the Sikorsky H-19. The evaluating pilots and sonar operators determined that the dipping sonar was able to detect and track submarines and, after some redesign to decrease pilot workload (no need for newspapers anymore) and make the sonar more lightweight and compact, the Navy accepted the AN/AQS-4 in 1952. The pilots and sonar operators who trained on the new helicopter sonar package, became members of the first two Naval Helicopter Anti-Submarine Squadrons: HS-1 Seahorses and HS-2 Golden Falcons.

The legacy of those first HS squadrons persists. The Golden Falcons still exist today, redesignated as HSC-12 in 2009. The technology, though more advanced, exists today as well. The AN/AQS-4 was the predecessor of the AN/AQS-13 dipping sonar, utilized for nearly 50 years on helicopters such as the SH-3 and the SH-60F, and the predecessor of the AN/AQS22, the current dipping sonar aboard the MH-60R.

The unique role of helicopters in ASW has developed over generations of aircraft and aircrew. The development of sonobuoy employment and processing capabilities, magnetic anomaly detection, lightweight torpedo carriage, more robust acoustic processors, and more advanced tactics has made helicopters vital assets from ship or shore to hold enemy submarines at risk.

Today, U.S. Navy Helicopter Maritime Strike squadrons are deployed around the world, sharpening their skills against submarines and standing ready for the next fight.