A Mk 10 torpedo fitted with a Mark 6 magnetic influence detonator passes under the target, a decommissioned submarine, without exploding in the first of only two live-fire tests of the Mark 6.
(U.S. Navy photo courtesy of Norman Polmar).
by John Patrick
The torpedo failures that American submariners suffered in World War II are rightly infamous, but that experience was not unique to America. Even Germany, the leading submarine power for most of the war, suffered failures just as devastating.
Submarines became Germany's principal naval force in World War I. With the battleships of Imperial Germany's High Seas Fleet unable to break the blockade imposed by Britain's Royal Navy, the Germans resorted to unrestricted submarine warfare in an attempt to strangle Britain's commerce and knock her out of the war. They nearly succeeded. Armed with relatively simple torpedoes, the U-boats sank millions of tons of Allied shipping before the Royal Navy and the U.S. Navy managed to defeat them with convoys.
After the war, the victorious Allies abolished the German submarine force, but they could not prevent German submariners from developing new technology. Despite extremely tight budgets, the submariners secretly commissioned designs for improved U-boats and sponsored the development of advanced torpedoes. These covert initiatives bore fruit in the wake of the 1935 Anglo-German Naval Treaty, which allowed Germany to begin rebuilding its submarine force.
Germany entered World War II with two state-of-the-art submarine torpedoes: a traditional "steam" torpedo powered by a mixture of air, water and liquid fuel; and the world's first operational electric torpedo, which left no wake to alert the target or reveal the U-boat's location. Both torpedoes had a warhead larger than those of World War I, and both had a "magnetic pistol" detonator activated by a target ship's magnetic field. The new detonator was designed to explode the warhead just as the torpedo passed beneath the keel. Adm. Karl Dönitz, who led Germany's pre-war submarine buildup, was confident this new form of attack would prove devastating.
Loss of Confidence
The first doubts about the effectiveness of German torpedoes cropped up early in September 1939, the first month of the war. U-39 got a good set-up on the British aircraft carrier Ark Royal, launched three torpedoes, and went deep. Hearing three well-timed explosions, the crew assumed three hits, but U-boat headquarters soon learned that Ark Royal was still operating and concluded that the magnetic influence detonator had activated prematurely. Not long afterwards, another U-boat visually observed several "prematures."
Dönitz referred the matter to the Torpedo Directorate, which recommended resetting the detonator to reduce its sensitivity. Despite further adjustments, reports of prematures continued, including two cases of explosions close enough to endanger the launching boat. Yet some torpedoes, like those that sank the British carrier Courageous, seemed to work fine. With many sub crews still green, the Directorate attributed most failures to poor maintenance or poor shooting.
However, 13 U-boat commanders, including some of the best, reported malfunctions in the war's first month, leading Dönitz to conclude that crew errors could not explain all of the failures. He prevailed on the naval high command to order a technical investigation. The Torpedo Directorate found a wiring flaw in the influence detonator and signs of a mechanical defect in the steam torpedoes that could not yet be isolated. The wiring was fixed. In the steam torpedoes, the influence detonator was disconnected, leaving only the impact detonator. But in October, the war's second month, one boat reported no less than seven torpedo malfunctions in a single engagement. Acting on his own authority, Dönitz, on Oct. 18, ordered his boats to cease using the obviously defective influence detonator altogether.
Many U-boat commanders suspected that torpedoes were running too deep. The Torpedo Directorate had known for some time that torpedoes were running six-and-a-half feet deeper than intended because the exercise heads used for calibration were more buoyant than warheads. Directorate officials thought this would make no difference with the influence detonator, but as soon as they learned that the U-boats would be using only impact detonators, which required more precise depth-keeping, they notified the submariners of the problem.
Dönitz then received a report from a boat in the Mediterranean that four impact detonators failed in an attack on a stationary ship under ideal conditions. The high command ordered another technical investigation, and on Nov. 10, Dönitz directed all boats to use a supposedly improved version of the influence detonator. Later that month, a boat reported that three steam torpedoes with influence detonators had prematured—two close aboard—and one electric torpedo failed to detonate. Another boat tallied nine failures in 11 launches.
"The torpedo," Dönitz bitterly concluded, "can no longer be regarded as a front-line weapon of any use."
German G7a "steam" torpedoes being repaired in 1940. (Photo courtesy of Établissement de Communication et de Production Audiovisuelle de la Défense, Paris, France).
Fixing the Problems
Having lost confidence in the torpedo establishment, the German Navy replaced the head of the Torpedo Directorate and appointed an outside civilian engineer to control all torpedo work, including badly lagging production. The new leadership quickly identified several technical defects, but fixing them would take time.
In March 1940, Hitler ordered most available U-boats to Norwegian waters to intercept an anticipated Franco-British occupation force. The Germans invaded Norway on Apr. 9. Convoys carrying the Allied troops began to arrive soon afterwards, but the U-boats lurking offshore missed one opportunity after another to sink Allied ships. Subsequent analysis indicated that defective torpedoes prevented them from scoring hits in at least one attack on a battleship, seven attacks on cruisers, seven on destroyers, and five on transports.
On May 1, the torpedo experts announced a high failure rate in tests of the "clumsy" and unnecessarily complex impact detonator, whose defects had gone undetected due to inadequate prewar testing. On May 5, the Germans captured a British submarine complete with torpedoes, and the Torpedo Directorate agreed to copy the superior British impact detonators. Later in May, continued problems with supposedly improved influence detonators led Dönitz to forbid their use until all their problems were unquestionably solved, which would not happen until much later in the war. However, starting in June 1940—the war's tenth month—sinkings with the new impact detonator rose dramatically.
One problem remained undetected until America entered the war in December 1941. U-boats that made the long transit to attack shipping along the U.S. East Coast began to experience numerous electric torpedo failures. On Jan. 30, 1942, a young skipper reported that while ventilating electric torpedoes onboard, his crew discovered leakage into the balance chamber housing the torpedoes' depth-setting equipment, which caused a pressure increase that could make them run deeper than set. The Torpedo Directorate confirmed the problem, which tended to worsen during long periods at sea, and recommended successful fixes.
Thus, nearly two and a half years into the war, the saga of German torpedo malfunctions came to a close just as American submariners were discovering similar failings in their own torpedoes. Like the German problems, the failings of American torpedoes stemmed from poor or unproven designs whose problems went undetected due to inadequate technical and operational testing.
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