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In This Issue...........Page

Reprint. Silent Victory....1, 4-6

2013 Contributors. ...........2-3

President’s Message............ 3

Personnel Directory............. 6

Vol Contributor. Mark 6 Magnetic Influence Exploder ..........................................7-13

A Bit of Undersea History...


by Ralph Enos Reprinted from Undersea Quarterly, Winter 1995 In the winter of 1944-45, United States submarines wrapped up their victory over the Imperial Japanese Navy and Merchant Marine. The next six months of war would add little to American submarines’ tonnage totals as they scavenged the western Pacific for increasingly scarce targets. The burden of the war of blockade against Japan’s commerce would now pass to carrier aviation and to B-29 bombers delivering mines into Japanese home waters. Let us review the achievements of this campaign, shed some light on little-appreciated aspects of it, and dispel some myths. The principal achievement of US submarines in World War II was strangling Japanese importation of vital commodities, particularly oil. Japan is an island nation, dependent on seaborne commerce for most of its fuel, food, and raw materials for its industry. Cut off this commerce and its industrial machine, its capacity to wage war comes to a halt. The United States succeeded in doing this where Germany twice failed, in two world wars, to do the same thing to another industrial island nation, Great Britain. But commerce warfare was not the way war against Japan was planned by the US Navy before the fact. The United States had

Museum Store................14-16



WINTER 2013 Volume 17, Number 4 Undersea Quarterly is the newsletter of the Naval Undersea Museum Foundation. It is published quarterly by the Naval Undersea Museum Foundation in Keyport, Washington. The Naval Undersea Museum Foundation is a private, nonprofit, charitable corporation dedicated to supporting the Naval Undersea Museum. The foundation is not a part of nor sponsored by the Department of Defense or the U.S. Navy, which operates the museum.



The Foundation gratefully acknowledges contributions made in 2013 to the museum by individuals, businesses or other organizations.

Foundation Associate RADM Herbert M. Bridge, USNR (Ret) and Ms. Edie Hilliard RDML Craig Dorman, USN (Ret) Dr. & Mrs. Wayne M. Sandstrom Mr. James R. Sisley Patron Mr. Robert L Cannon RADM & Mrs. George W. Davis, USN (Ret) CAPT & Mrs. Robert Hoag, USN (Ret) Navy Region Northwest Mr. & Mrs. Paul S. Thiebaud Naval Undersea Museum 1103 Hunley Road Seat in the Future Silverdale, Washington 98315-1103 The Buell Family Levels of Giving 360/396-4148 Fax: 360/396-7944 John D. Buell Foundation Associates: $1000+ Mrs. Patt Hannan Seat-in-the-Future: $500 each Director: Mrs. Lindy Dosher; Education: Dennis and Patt Hannan Patrons: $500-$999 Mrs. Valerie Johnson; Curator: Mrs. Pearl Harbor Survivors Mary Ryan; Exhibits: Mr. Jarrod Gahr Benefactors: $250-$499 CAPT Charles H. Wilbur, USN Collection Management: Mrs. Jennifer Builders: $100-$249 In recognition of William Galvani Heinzelman and Mrs. Lorraine Scott.; Providers: $25-$99 Operations Manager: Mrs. Olivia Wilson; Benefactor Facilities/Data Entry: US Navy personnel Mr. & Mrs. John H. Dalton Mr. John C. Dimmer Naval Undersea Museum Foundation CDR & Mrs. Ronald Krell, USN (Ret) P.O. Box 408 Mr. & Mrs. Thomas L. Lewis Keyport, Washington 98345 Builder 360/697-1129 RADM Robert L. Baker, USN (Ret) Mr. & Mrs. James Bell President: RADM Bruce A. Harlow, Michael P. Berman JAGC, USN (Ret); Executive ViceMr. & Mrs. Burton O. Boyd President, West: Vacant; Secretary/ Treasurer: Ms. Bettye J. Shifrin; General Dr. Anna H. Chavelle, M.D. Counsel: John A. Bishop; Trustees: Mr. Mr. John Csirke Robert Anderson; Mr. John A. Bogen; CAPT Jack G. Fletcher, USN (Ret) CAPT Larry Carter, USN (Ret); Mr. Ms. Elise Gillette Donald Chalupka; RADM George W. Mr. & Mrs. Morton O. Heinrich Davis, VI, USN (Ret); RDML Craig Mr. Richard D. Helander Dorman, USN (Ret); RADM Bruce Ms. Susan Kuehne Harlow, JAGC, USN (Ret); CAPT Robert Mr. Robert J. Kuehne Hoag, USN (Ret); CAPT Ronald Krell, USN (Ret); CAPT Michael Mathews, USN RADM WH Langenberg, USNR (Ret) (Ret); Mr. Bruce Riggins; Vice Presidents: Mr. & Mrs. Richard LeVon Mr. Theodore Barreaux; Mr. Alan Beam; Mrs. Amanda Loveless Mr. Will Lent; Dr. Wayne Sandstrom; CAPT Stanley Marks, USN (Ret) CAPT Charles Wilbur, USN (Ret) Mr. & Mrs. Rodney L. Mash Executive Assistant: Ms. Bettye Shifrin Mr. & Mrs. Clarence Moore Museum Store Manager: Mr. & Mrs. Bruce Riggins Mrs. Daina Birnbaums Ms. Ann Sisley Undersea Quarterly Editor: Mr. G.E. Thornton Ms. Bettye Shifrin Mr. James Vorosmarti Mailing/Membership: Mr. John Bogen Printing: Kitsap Printing CAPT Charles H. Wilbur, USN Printed on recycled paper Š 2013 NUMF CAPT Christos Zirps, USN (Ret) CONTINUED ON PAGE 3

3 WINTER QUARTER 2013 From the President...



Bruce Harlow

My message to you all this time will be brief and sincere. Especially at this time of the year, it is important to remember those who are contributing to the success of our nation – our service men and women – who daily guard our shores, our air, our waters from any and all enemies. These honorable people may be away from their families, they may be in harm’s way. I would ask you to remember them in your prayers, in your hearts, and in any other way you see fit. We also should remember those who have served in the past and those who made the ultimate sacrifice for the freedom of our nation. My personal thanks to you all and best wishes for the New Year. BRUCE HARLOW

2013 CONTRIBUTORS The Foundation gratefully acknowledges contributions made in 2013 to the museum by individuals, businesses or other organizations. Provider CDR John Alden, USN (Ret) CDR Frederick Bereswill, USNR (Ret) Mr. Thomas Berg Dr. & Mrs. Jaap W. Boosman Mr. Charles G. Brunnquell Mr. Robert C. Burritt Mr. Roy D. Carter Mr. & Mrs. Clifford L. Clark Mr. & Mrs. Lewis Coleman CAPT & Mrs. Robert Davis, USN (Ret) LCDR R. A. Dungan Mr. Brett S. Dungan

Mr. James J. Green Mr. William D. Hahn Mr. & Mrs. Walter Hoeg Mr. & Mrs. Marwin E. Holm Mr. & Mrs. George W. Hooper Mr. Nick F. Ierise Mr. Lawrence S. Justason Mr. William J. Keiderling Mr. Ernest LeVon Mr. & Mrs. Ernest H. Linger Mr. John C. Lynch CAPT & Mrs. TM Mahony, USN (Ret) CDR R. Bruce McComb

CDR Richard C. McCrory, USNR (Ret) Mr. & Mrs. John Nyquist Mr. & Mrs. Larry J. Porter Mr. & Mrs. Dwight E. Roof Ms. Katie Sell Mr. & Mrs. Robert Singer Mr. James Smalley Ms. Helen Langer Smith Mr. A.V. Stevens LT Thomas N. Thompson, USN (Ret) CAPT & Mrs. D. C. Welling, USN Mr. Ray W. Whitmore Dr. & Mrs. Charles R. Zentner

ALFRED GANGNES Gifts in Kind Newsletter Team -John Bogen -Joe Ekstedt -Frank Hutson -Dick Levon -Art Schrom Exterior Planters -Caroline Hoag -Bremerton Garden Club

Professional Services -Kathie Barbaro, CPA The Volunteer Staff Foundation Board Members Newsletter Contributors -Jerry E. Armstrong -Bill Gluth -Charles Gunderson -Darlene Iskra -Larry Tucker

The Foundation would like to express our sympathy to the family of Al Gangnes who passed away recently. Al was a valued member of the foundation board for many years; his welcoming smile and positive personality will be missed by those of us who were privileged to know him. In Memory of Alfred Gangnes Ms. Lula Belle Jenkins Lane Powell PC




foreseen the possibility of war with Japan for 25 years before December 7, 1941 and had developed a sophisticated war plan, code-named “Orange”, on how it would be waged. Plan Orange called for progress of the undivided US battle fleet across the Pacific to engage and destroy the Japanese battle fleet. Submarines had roles as pickets, scouts, and distant escorts for the fleet, and were assigned to the scouting force. US submarines had to be designed with characteristics that suited these tasks. The resultant design was called the “fleet” submarine because it was optimized for its fleet support role. Fleet submarines had to have great endurance, high surface speed (to keep up with the battle force), and good sea-keeping ability (since they would spend most of their time running at high speed on the surface). After 20 years of wrestling with this problem, US submarine designers—sensing that war with Japan was imminent—in 1940 settled on one design for serial production, the Gato class.

The Gatos were 311’9” overall with a beam of 27’3” and a draft of 15’3”; displaced 1,526 tons surfaced and 2,424 tons submerged; and were powered on the surface by four 5,400 hp diesels and submerged by two 2,740 hp DC motors, which gave them a top surface speed of 20 knots and submerged speed of 9 knots. They had 10 torpedo tubes, six forward and

four aft, and carried 24 torpedoes, a huge armament load made possible by the sub’s large size. The large size was necessary to house the four diesels and extra fuel tanks that gave the boats 11,000 mile range at economical speeds. Later in the war, the Balao/Tench classes were introduced with the same external characteristics as the Gatos, but with 400 ft operating depth vs. 300 ft in the Gatos. Altogether, 242 of these classes were built between October 1940 and the end of the war. Plans for fleet submarine escort and support missions were scrapped when the US battle fleet was crippled at Pearl Harbor. American submarines were untouched, and in the months immediately after the attack, they and the also untouched carrier fleet were the only offensive capability the US had in the Pacific. The submarine force had a new mission thrust upon it: US submarines were immediately sent on offensive patrols in Japanese home waters. Several squadrons of submarines had been sent to the Philippines before Peal Harbor and constituted the principal force of the United States Asiatic Fleet. When Japan attacked the Philippines, these submarines sortied to defend against the invasion. They accomplished very little. Eventually, when naval operations from Philippine bases became untenable, these subs repaired to Australia from where they, or their replacements, operated for the rest of the war. US submarines operating from bases at Brisbane on the east coast and Fremantle on the west coast of Australia came under the command of the Southwest Pacific Theater Commander. Histories of the US Pacific submarine campaign have tended to focus on Pacific Fleet operations out of Pearl Harbor. But SoWesPac subs were a major force in the campaign, sinking one third of the total tonnage and losing 19 boats in the process. CONTINUED ON NEXT PAGE





American submarines accomplished little during the early months of the war, in the Philippines and elsewhere. This was due, among other things, to excessive caution on the part of some incumbent skippers, tactical doctrine that focused on submerged attack using sonar only, a severe shortage of torpedoes, and defective torpedoes. Poor reliability of the Mk 14 torpedo was a major reason why US submarines were not as effective as their numbers and skills would seem to assure before the middle of 1943. They had large numbers of magnificent boats, well-trained and well-led crews, aggressive skippers, and operational flexibility that German U-boat commanders would envy. Moreover, American cryptanalysts were able to break most Japanese naval codes, and often gave precise information on target location and movements. But the torpedoes wouldn’t work right. The defective torpedo problem was not easy to solve. In fact, there were multiple problems, the problems sometimes masked each other, there was official reluctance to accept torpedo failure as an excuse for poor operational performance, and there was a reluctance to expend precious torpedoes in testing. The principal culprit turned out to be the Mk 6 exploder, designed to do greater damage to a surface target by exploding under the target’s keel, and which was set off by a magnetic sensor. It had been developed in great secrecy before the war and insufficiently tested. The Mk 6 had a backup contact exploder that was also defective. Eventually, the magnetic feature was disabled, the contact exploder was fixed, and the force got on with its business of sinking Japanese ships. By mid-1943, the Japanese navy was severely crippled by losses in the long struggle for control of the Solomon Island chain and the carrier battles of Coral Sea and Midway. Naval targets for US submarines became rare, and the force began to seek merchant ship targets. Willy-nilly, US submarines had stumbled onto the strategy that would defeat Japan. Many new long-range Gatos were now available to patrol Japanese “choke points” in the Taiwan Straits, and the East and South China Seas. Tankers, carrying vital oil and

other petroleum products to Japan, began to be sunk in large numbers. By the end of 1944 submarines had virtually cut Japan off from its resource-rich conquests in Indonesia, Malaya, and Indochina. Between January 1944 and the end of March 1045, US submarines sank 86 tankers of over 523,000 tons. (By contrast, in all of 1942 and 1943 only 21 tankers of 148,000 tons were sunk.) Without oil, an industrial nation necessarily must stop functioning. The last shipment of oil from the south reached Japan at the end of March 1945. In all, US submarines sank 1,314 Japanese ships totaling 5.3 million tons. Of these, 201 were naval vessels, including one battleship, eight carriers, and eleven cruisers. Japan’s merchant marine was all but wiped out, losing 70,000 men in the process. This devastating maritime victory was accomplished by a submarine force that numbered a maximum of 50,000 men including shore and tender support. This force—amounting to only about 1.5 percent of total Navy uniformed personnel in the war— was responsible for 55 percent of Japan’s maritime losses. In addition, submarines rescued 504 downed allied aviators. It did not come without a price. Fifty-two US submarines and 3,500 men were lost, 22 percent of the total that went on patrol. This was the highest casualty rate of any arm of the US armed forces. The US submarine force effected calling itself the “silent service” allegedly after newspaper reports revealed that Japanese depth charges were being set too shallow to damage our submarines. Submarine force commanders from then on dropped a veil of silence over their operations, an attitude that prevails today. However much there might have been good operational logic for this attitude, it became a public relations problem for the submarine force. The contribution of the submarine force to the US victory in the Pacific was enormous. But you would never know it from reading the papers. Highly visible—and deserving—sea service forces like carrier aviation, amphibious units, marines, and Atlantic fleet sub-hungers got the glory. The submarines’ “silent victory” went unsung. CONTINUED ON NEXT PAGE





How was it that US submarines were able to do to Japan what Germany tried so hard and failed to do to Great Britain? Japan’s response to the submarine challenge was one reason. Japan never gave ASW the priority it deserved considering its geographic and strategic situation—and which Great Britain most decidedly did. Japan never provided enough ASW escorts, its convoys were inefficient and poorly executed, its ASW tactics were poor. America had the advantage of reading Japanese coded signal traffic, whereas in the Atlantic the opposite was true: Britain and the US were reading the U-boats’ mail. US submarines were superb ships for the job they fell into. Characteristics of the fleet submarine developed for entirely different reasons proved to be just what was required for long transits to distant patrol areas in the vast Pacific: high surface speed, great endurance, relatively roomy accommodations, lots of torpedoes. Finally, credit for America’s submarine “silent victory” must be given to the men who manned these boats. America’s World War II submariners— like those of today—were an elite group of sailors who consistently got more from their equipment and weapons than was expected. Operational performance was a synergistic combination of equipment and human beings; the result being greater than the sum of its parts. The recent

sobriquet, “Steel Boats, Iron Men”, is not idle hyperbole. The contributions of American undersea warfare to the defeat of Japan have been under-reported and under-appreciated. We have already detailed in these pages the contribution to Japan’s demise of the mining campaign in Japanese home waters called Operation Starvation (NUMF Newsletter May 1985). This campaign, which sank or damaged 1.4 million tons of Japanese shipping, completed the strangling blockade of Japan started by our submarines. By August 1945, the Japanese homeland was cut off by American Sea power, without fuel to fly anything but suicide bombers, without food to feed its people. Defeat was inevitable. Much is being written about how the 50th anniversary of the end of the war should be remembered, particularly how the atomic bombing of Hiroshima and Nagasaki is to be treated. The Navy’s submarine service has no such ambivalence. It knows that its “silent victory” created the conditions that preventing Japan from continuing the war. It may not have been planned that way in the beginning; today it may be little appreciated, but this should not detract from the achievement. In the words of Theodore Roscoe in US Submarine Operations in World War II, “The atomic bomb was the funeral pyre of an enemy who had been drowned.”

Personnel Directory Websites Naval Undersea Museum.......................... Naval Undersea Museum Store....... Navy Band Northwest............ Foundation Personnel email addresses Undersea Quarterly Editor, Foundation...... Daina Birnbaums, Museum Store.......

NUM Personnel email addresses Lindy Dosher, Museum Jarrod Gahr, Education...................................... Jennifer Heinzelman, Collections Valerie Johnson, Mary Ryan, Lorraine Scott, Collections Management........ Olivia Wilson,


THE MARK 6 MAGNETIC INFLUENCE EXPLODER, A LITTLE PREMATURE. Charles R. Gundersen & Jerry E. Armstrong, April 26, 2012. Published by the Naval Undersea Museum

Too Little Pre-War Testing Such a new device as the influence exploder begged for testing to assure it operated as predicted. But depression-era budgets for testing were very restricted and the Navy approved no live fire testing of the Mark 14 torpedo against real targets (unless Newport could return both target and torpedo to operational condition).1 Expending test articles during an exercise where both weapon and target were destroyed was prohibitively expensive. Hence, very limited testing was done. Newport was only able to conduct one SinkEx. Amazingly, the Bureau of Ordnance gave Newport a submarine to use as a target for testing a weapon designed to sink battleships. This 1926 test was the only time the magnetic influence exploder was used to detonate a torpedo warhead at sea prior to World War II. More testing was conducted off South America in 1933 under the direction of Ralph Waldo Christie, who not only was instrumental in developing both the Mark 6 exploder and the Mark 14 torpedo, but also advocated their thorough testing. But these tests did not involve warshot torpedoes against steel hull ships. This series of tests looked at how often the Thyratron tube tripped as the exercise torpedo passed under USS INDIANAPOLIS (CA35). “Everyone, particularly Christie, seemed to be impressed with how consistently the exploder tripped.”2 One big assumption made by Newport early in the program was the shape of the magnetic distortion field directly under a ship. It was assumed that the influence of the ship’s magnetic field upon the earth’s field would produce a hemispherically shaped distortion pattern. However, this was not the case in the low magnetic

1 Newpower, 30. 2 Gannon, 80.

latitudes where the earth’s lines of magnetic flux are nearly horizontal. At these locations the pattern of the combined fields flattens out to a disk shape that is shallower and broader than the assumed hemispherical shape. In more northern magnetic latitudes the distorted combined fields may well be more hemispherical in shape and extend deeper under the keel. This issue was to become very important when setting the depth index on the torpedoes to have them run at a particular depth under the keel. To measure the run depth of an exercise torpedo a Depth and Roll Recorder was installed in the torpedo’s exercise head. Also, the torpedo itself had its own depth sensor (the Uhlan gear) to drive the torpedo down to its operating depth. However, mainly due to a lack of understanding regarding the hydrodynamic flow past the inlet ports of these two depth sensors, both of these devices gave false readings. Had the Depth and Roll Recorder worked properly, a more complete three-dimensional picture of the testing run could have been obtained. Therefore, there was no accurate or independent method available to measure depth; either before the war or during the critical early months when the fleet was plagued with torpedo misses due to torpedoes running too deep. In addition, test firings “could not determine whether or not firing mechanisms in torpedo warheads would have caused the torpedoes to explode, an on-going problem with the Mark 14 torpedoes used by submarines in the Pacific during World War II.”3

3 Frank Snyder, Captain, USN (Retired Naval War

College Professor), “A Gould Island Chronology, And Some Associated Historical Notes,” Torpedo Testing sidebar, Occasional Paper No. 3. Jamestown Historical Society, Jamestown, RI (Aug. 9, 2003): 5. CONTINUED ON NEXT PAGE





It wasn’t until October 1941 that fleet submarines received the complete Mark 14 torpedo with the Mark 6 Magnetic Influence Exploder. However, the exploder was not a big hit with the operating forces as on June 24, 1943, it was deactivated on all submarines under the command of Vice Admiral Charles A. Lockwood, Commander, Submarines Pacific (ComSubPac). Why It Didn’t Work After discovering the two drawings in Figures 1 and 2, (reprinted on Page 9) the authors of this paper tried to find out what exists in the open literature that could explain how the magnetic influence exploder worked, that described the electric circuit, and that explained (from the circuit’s point of view) how the exploder could have failed. Since no complete explanation was ever found, here is our summary of the possible causes behind the problems with the exploder, based on our review of the circuit drawings and from our literature search. It is hoped that these comments will aid in the understanding of this beleaguered device. One consistent problem with any device designed for undersea use is seawater leaks. This can best be explained by the experience on board USS SCORPION (SS 278). They assumed a leak path existed around the impeller’s rotating shaft and, as a result, they tightened the packing gland seal more than specified. This unauthorized change allowed them to achieve a one-third higher hit rate than the fleet average at the time and prevented any further prematures.4 The packing gland seal was an interference type of seal (O-rings not being in general use at that time) and worked by pressing against both the rotating shaft and stationary opening in the base plate. But, tightening this watertight packing gland might have slightly restricted the rotation of the impeller shaft. If the impeller’s rotation had been slowed down, it would have extended out the torpedo arming distance and given the torpedo more time to settle down following any harsh launch dynamics (assuming the target was still outside this new arming distance). This would have led to improved performance of the

4 Newpower, 146.

weapon. BuOrd even wanted the arming distance extended out to about 700 yards.5 At shallow running depths the leak would have been most prevalent, but the deeper the torpedo ran the more seawater pressure would have been applied to the packing gland seal and the better it would have sealed against leaks. We believe this leak path was a strong probability and the subsequent tightening of the seal would have been the proper response to the problem of seawater leaks and should have been a standard procedure on all Mark 6 exploders. Another important failure mechanism was deep running. The torpedoes “were running an average of 11 feet deeper than set. This could make a whale of a difference in the performance of our magnetic exploder ….”6 The exploder was designed to work best when the torpedo was set to run below the ship with no intention of actually hitting the ship, which would have allowed the contact exploder to fire the torpedo. In 1942 BuOrd recommended setting torpedoes to run 10 feet under the keel of battleship size targets.7 Adding in the 11-foot depth error put the torpedo 21 feet under the keel. Evidently this was just too far away and the target was out of reach. At this depth any weak change in magnetic field intensity would not produce sufficient voltage change at the grid element of the Thyratron Tube to trigger it. The general design of the exploder seems too delicate, too sensitive for normal operational use. At 10 feet below the keel an exploding warhead was expected to break the back of a large ship, but at 21 feet below the keel there may be no explosion at all or one too weak to be effective And things didn’t get any better when the deep running problem was corrected by raising the running depth of the torpedo. With the torpedoes now running at their optimum depth, it was

5 Buford Rowland and William B. Boyd, U.S. Navy

Bureau of Ordnance in World War II Chapter 6, Torpedoes (Washington D.C.: Bureau of Ordnance, Department of the Navy, 1953), 104. 6 Charles A. Lockwood, Vice Admiral, USN, Sink ’Em All, Submarine Warfare in the Pacific (New York, NY: E.P. Dutton & Co. Inc., 1951), 21. 7 Rowland and Boyd, 103. CONTINUED ON NEXT PAGE





expected that the sink rate of Japanese ships would increase. However, this was not the case (see the Appendix in the original document for a sink rate analysis). Instead they went off a little too prematurely. About 10 percent of the torpedoes fired were prematures; not a lot compared to the total number of torpedoes that functioned properly, but enough to be noticed since the effect could be so disastrous for the FIGURE 1 attacking submarine.8 We have identified three areas along the track where prematures occurred: • In this first case the torpedo goes off right out of the chute, at roughly the arming distance. That torpedo’s exploder mechanism being so sensitive it goes off as soon as it can (due to either seawater leakage or an improper adjustment for the local magnetic conditions). • This is the case where the premature detonaFIGURE 2 tion happened anywhere along the track to the target. And if this track was at a shallow depth, 12 feet or less, and in heavy seas prematures were more likely to occur. High sea states would cause the nose of the torpedo to oscillate vertically (in heave or pitch), thus causing the Pick-Up Coil to cut through the earth’s magnetic flux lines by swinging up and down. If the motions were large enough, the generated output voltages could reach the critical amplitude at the grid element that trips the Thyratron Tube. Normal oscillations in the earth’s magnetic field are shown as points labeled “A,” “B,” and “C,” in Figure 5. But larger vertical motions (pitch), due to heavy seas, or horizontal motions (yaw), due to course changes, can cause the

8 Rowland and Boyd, 104.





THE MARK 6 MAGNETIC INFLUENCE EXPLODER Pick-Up Coil to move more rapidly through the magnetic field and, if these motions are severe enough, point “P1” can be reached and the Thyratron Tube could trip. • In this third case the detonation does not occur close enough to the hull. The magnetic field pattern under battleships was thought to be hemispherical in shape. So the aim point of the torpedo was at a point where the hemisphere extended the deepest under the hull, which was under the keel. On these large targets, it was thought that setting the torpedo run depth to 10 feet under the keel would produce a detonation at point P4 in Figure 5.9 Up until 1942 Newport believed that their information indicated that a magnetic gradient sufficient to cause the exploder to fire rarely extended more than a few feet beyond the beam of the target ship making pre-

9 The shape of the target’s magnetic field is not shown in Figure 5.

matures very unlikely (indicated as point P1 in Figure 5).10 It was feared that setting torpedoes to run shallow would have them harmlessly explode against the heavily armored side plating of Japanese capital ships, but setting them lower would unleash some type of Japanese countermeasure. But what really caused this type of premature was a misunderstanding of the shape of the magnetic field. The actual shape was that of a flattened hemisphere, more like the shape of a pancake (as mentioned before). Horizontally, the shape was not circular but was extended in the north and south directions and shortened in the east and west directions. This pattern (especially in the north and south directions) did, in fact, act somewhat like a countermeasure by causing the torpedo to detonate about 50 feet from the target’s hull; prompting Vice Admiral Lockwood to quip, “I hope they don’t tell

10 Ordnance Pamphlet No. 663, 100–101.






us we have to shoot ‘em only on east and west headings!!”11 One effect of an explosion close to the hull was that it looked like a good hit when viewed by the submarine captain through the periscope In any case, the effect of prematures on the submarine could be disastrous. In addition to not causing any harm to the enemy, a premature warned the target ship of an attack and it pointed out the direction of the attacking submarine. The location of the attacker was at the beginning of the trail of torpedo exhaust gas bubbles. The shock wave from a premature could affect the track of other torpedoes in a salvo and cause them to miss. Also, prematures warned the target ship in time to turn away from the next salvo of torpedoes. Following alertment the enemy ASW escort ship invariably aimed directly for the submarine with the often result being a disastrous depth charge pounding.

11 Newpower, 136.

The resultant depth charging from an enemy ASW escort may have “contributed to the loss of one or two American submarines.”12 Finally there was a major problem due to the geographic location difference between the submarine operating area and the Naval Torpedo Station at Newport where the device was developed and many of its testing occurred as shown in Figure 6. Newport is close to the North Magnetic Pole where the lines of magnetic flux are closely spaced and vertical, and the submarine operating area is near the Magnetic Equator where the flux lines are more widely spaced apart and horizontal. The direction of these lines affects the shape of the magnetic fields under the steel hulls of ships. This field was assumed to radiate in all directions an equal amount to form a perfect

12 Theodore Roscoe, United States Submarine Opera-

tions in World War II. Chapter 20, Torpedo! (Annapolis, MD: U.S. Naval Institute, 1949), 256.





THE MARK 6 MAGNETIC INFLUENCE EXPLODER hemisphere below the keel, as already mentioned. Knowledge of how deep this hemisphere extended below the keel would allow the torpedo’s depth to be set properly, and the resulting explosion would occur directly under the keel and break the ship’s back.13 This was the aim point. However, this aim point moved around as the ship sailed to different latitudes. Near the magnetic poles the shape of the hemisphere was elongated vertically (somewhat like a cone). The flux lines were more concentrated and ran nearly vertical, tending to pull the ship’s magnetic field down. Near the magnetic equator the earth’s magnetic flux lines ran nearly horizontal in a north and south direction and were more spread out and the magnetic field under the ship flattened out. Also, near the equator, the shape of the field bulged out in a north and south direction and shrank in an east and west direction, as influenced by the earth’s lines of magnetic flux. The effect was to prevent the ship’s “target size” from reaching down very far under the keel (possibly not even extending down 10 to 15 feet under the hull). By “target size” it is meant the ship’s magnetic field (that perfect hemisphere) as deformed into the pancake shape by the presence of the earth’s field. Torpedoes running shallow and approaching from a north or south direction would often run into this extended field while still some 50 feet, or so, from the hull and detonate prematurely.14 Did it ever work? If the torpedo made it to the target and was at just the right depth and magnetic latitude, if it encountered a magnetic field of just the right size, and if the target was on just the right magnetic heading so the field in the direction of the torpedo was very close to (or even somewhere under) the hull, it might explode. However, things did improve with time. As each torpedo problem area was corrected the overall rate of sinking did increase slightly. An analysis of the improving sink rate is given in the Appendix of the original document.

13 Keith Wheeler and the Editors of Time-Life Books.

War Under The Pacific, World War II. Chapter 1, A Force Unready For War (Alexandria, VA: Time-Life Books, 1980), 46. 14 Douglas Murphy, “Hit or Miss,” American Heritage of Invention & Technology, Vol. 13, No. 4. (New York, NY: American Heritage), Spring 1998, 56.

Solutions Taken By The Fleet The action taken by the operating forces was to shut it down. One submarine skipper deactivated the exploder on his own initiative, just one week into the conflict. Solutions Mandated By Submarine Command The submarine skippers may have wanted to stop prematures by deactivating the magnetic influence feature of the exploder, but the shoreside command wanted the exploder fixed and kept in service as it was thought this was the only way to sink a capital ship or a small shallow draft ASW escort vessel. The fleet prevailed and on June 24, 1943 the magnetic influence exploder was ordered deactivated on all PACFLT warships. BUORD’s Confusing Guidelines Among the not-very-helpful recommendations offered by BUORD were the following: • Don’t use the exploder in the southern hemisphere as at these latitudes a greater negative voltage would be impressed on the grid element of the Thyratron Tube, tending to reinforce its ability to prevent any current from flowing through the tube, preventing triggering. • New guidance was offered based on the size and shape of the target’s magnetic field. But, other than setting the torpedo’s depth, how could the sensitivity of the exploder be changed during an attack? • Again BUORD issued more instructions on August 31, 1943, requiring the current magnetic latitude, the target’s magnetic course, the target’s hull size (width and draft), and the target’s degaussing condition be added to the mix before the shot was fired.15 How were these new requirements to be implemented within the sealed magnetic exploder during the set up for the shot? To no one’s surprise the fleet would have nothing to do with this new formula. • And finally there is BUORD’s statement that the “magnetic exploder would work better if the torpedo could be allowed to run 700 yards instead of 450 before becoming alive.”16 This

15 Roscoe, 258. 16 Fletcher Pratt, “The Torpedoes That Failed” The CONTINUED ON NEXT PAGE




THE MARK 6 MAGNETIC INFLUENCE EXPLODER would preclude any close encounter shots, needed if the submarine found itself in the middle of a convoy or being chased by an ASW escort. This too was never implemented. Conclusion The problems with the Mark 6 magnetic influence feature plagued the submarine community for almost a year, lasting so long that by the time they were all cleared up, the new electric Mark 18 torpedoes were being introduced into the fleet and enemy targets were beginning to dry up. As more and more U.S. submarines came on line and began patrols in 1944, their patrol area was shrinking. So during 1944 there were more submarines, equipped with better gear (thus leading to more success), patrolling smaller areas that were containing fewer and fewer targets. And our torpedoes were working much better during the critical last half of the three-year submarine war against Japan, when Allied forces were re-taking the Pacific islands, MacArthur was island-hopping toward Okinawa, and the Pacific was teeming with our convoys filled with our own fat “targets”.17 The end of this first attempt at developing a proximity exploder for a torpedo came just two months before the circuit drawings shown in Figures 1 and 2 were released. The experience may have shown the concept to be valid, but its application was hindered by its lack of testing and the testing received during combat showed it to be a little premature for the war thrust upon it.

Atlantic, Vol. 186, No. 1, July 1950, 29. 17 “For all practical purposes, the U.S. submarine war against Japanese shipping ended in December 1944.” Clay Blair, Silent Victory: The U.S. Submarine War against Japan (Annapolis, MD: Naval Institute Press, 1975), 819.

SUPPORT YOUR FOUNDATION, YOUR MUSEUM Many of you, our foundation members, choose to support the museum because your careers were spent in our military and in defense contracting. Our volunteer staff comes to us as retirees from Keyport, as military spouses, as service retirees. Your life experiences while in the service are unique to each of you; your children and grandchildren may not know anything about what obstacles you encountered, what goals you achieved, where you were sent, even what you did on a daily basis before you became their parent or grandparent. These stories should not be lost. You are currently enjoying the contributions and suggestions from our volunteers and members. We would welcome the opportunity to publish articles, memoirs, photos—items that would be of interest to the naval history community. While we cannot promise to publish everything that is submitted, we would be pleased to hear from you at any time. The email address for the editor is and the mailing address is Naval Undersea Museum Foundation, PO Box 408, Keyport WA 98345. Think about where you’ve been. Think about the people you’ve met. Remember your comrades and the camaraderie you experienced. Then, write it down and send it to us.

Have you ever wondered what to give your parents, your grandparents, your grandchildren, your friends for their birthday, for the holidays, to acknowledge their retirement, to celebrate their anniversary? A membership in the Foundation is an excellent gift in so many ways. The articles and information in the newsletter alone are well worth the membership cost. A Seat-In-The-Future is another wonderful way to memorialize loved ones, fallen comrades, friends and significant figures in undersea history. A one-time gift of $500 entitles the donor to dedicate a plaque on the arm of a seat in the Jack Murdock Auditorium to someone of their choice. Naval Undersea Museum Fdtn P.O. Box 408 Keyport, WA 98345



From the Museum Store...


As the days grow shorter and the thermometer dips, we naturally want to stay inside where it is warm and cozy. At the Naval Undersea Museum Store, we have many items that will make winter indoors that much nicer! Cozy throws, the glow of scented candles, even battery operated LED candles (You’ll swear they’re the real thing!) Start the New Year out right with a calendar of reproduction vintage Navy football programs. This ingenious calendar contains 12 easily removable works of art which will fit in a standard 11x14 frame. It’s a calendar that keeps on giving! Combine it with our Army/Navy game day poster, a reproduction of the official program cover from the 1923 game for added impact. One of the most storied rivalries in sports, this is a year made famous for its rare score 0 – 0! While at this writing, we don’t have a score for this year’s game, I hope you all will join me in saying - GO NAVY! Science kits and puzzles for yourself, a child or grandchild. Educational, fun and a great way to spend time together! When making out your New Year’s resolutions, consider volunteering at the Naval Undersea Museum or the Museum Store. Museum Store proceeds benefit the Naval Undersea Museum Foundation which assists the museum with education programs, guest lecturers and volunteer events. Volunteers receive a discount at the store and work in a supportive, fun and interesting environment. Please contact Daina at 360-6971537, museumstore@ or DAINA BIRNBAUMS




I believe in the Naval Undersea Museum’s vision of the future and I want to help make it come true! I want to see the Museum complete with state-of-the-art exhibits, quality supporting facilities,and exciting educational programs. Please sign me up for the following: ___ Seat(s) in the Future $500 each Dedicated to_____________________________ Sustaining membership ___ Foundation Associate *$1000+ ___ Patron *$500-$999 ___ Benefactor $250-$499 ___ Builder $100-$249 ___ Provider $25-$99

Make checks payable to the Naval Undersea Museum Foundation (NUMF) VISA, MasterCard, American Express, Discover accepted. Card #___________________________ Exp ________ Signature_____________________________________ Send to: Naval Undersea Museum Foundation P.O. Box 408 Keyport, Washington 98345

*Donors of $500 or more may participate in the Seat-inthe-Future program by dedicating a seat in the Jack Murdock Auditorium for each $500 given. Other ___ As a one-time gift

Sustaining members receive regular quarterly newsletters, invitations to special events. The NUMF is a registered nonprofit 501(c)(3) organization. Gifts and memberships are tax-deductible for federal income tax purposes.

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Num 04 winter 2013