During the opening months of the Battle of the Atlantic, the Germans discovered that their updated magnetic torpedo detonators were malfunctioning in waters near the Arctic Circle. They correctly theorized that the Earth is a large magnet whose magnetism varies by location. They understood that different magnetic fields would surround a ship depending on its longitude and latitude. By mid-1941, the Germans had deactivated their magnetic exploders and were relying solely on contact detonators. The British soon followed suit. In a struggle as paramount as the Battle of the Atlantic, neither side could afford unreliable or ineffectual ordnance. American submariners, on the other hand, were just beginning a similar naval conflict in which they would not have reliable torpedoes for 18 months.

By August 1942, the faulty depth mechanism had been isolated and corrected, and the Mark XIV was striking more targets. Curiously, however, skippers began to report a large percentage of duds and prematures. Frustrated captains and crews now suspected the mysterious Mark VI detonator.

The submariners attempted to make in-field adjustments, in the process trying to accumulate sufficient evidence to warrant deactivation. Admiral Lockwood, now in charge of all Central Pacific submarines from Pearl Harbor, would have ordered immediate deactivation had it not been for the possibilities and flexibilities the Mark VI theoretically offered. When dealing with shallow-draft escort vessels, the under-the-keel shot was a must, and it was accepted that such a detonation against any size vessel was most effective. Early in 1943, however, the Bureau of Ships released a study contradicting that assumption. The study, based on Atlantic convoy sinkings, concluded that broadside hits that created instability were the most effective attacks against merchantmen, which lacked the armor belt and compartmentation of warships.

Since Japan’s lifeline was her merchant marine fleet and because the Bureau of Ordnance would only suggest slight technical adjustments to the Mark VI, Admiral Lockwood determined that the magnetic feature was more a liability than an asset. On July 24, 1943, he ordered his submarines to deactivate the Mark VI magnetic influence detonators and fire for contact hits only.

As later tests illustrated, the failure of the Mark VI design was twofold. In broad terms, the magnetic theory advanced by the Germans months earlier was correct. Depending on location, the magnetic field around a ship varies, and there were definate variances between the waters around New England where the Mark VI was tested and the southern Pacific. Additionally, internal construction flaws increased the chances of unreliable performance. Brush riggings, located on the generator that supplied power to operate the magnetic exploder, were discovered to be inadequate, and leaky base-plate castings allowed water into the exploder cavity. Having endured two major malfunctions in their primary weapon over a year and a half of disheartening combat, U.S. submariners eagerly abandoned the Mark VI detonator in favor of the contact mechanism. Fate, however, was to test their mettle one more time.

The contact device’s name alone suggested reliability and consistency. Although less advanced than the magnetic feature, however, the contact exploder was still a complex device with numerous parts capable of perplexing malfunctions. In fact, a malignant flaw in the contact mechanism had been hidden while other malfunctions were slowly and painstakingly resolved.

When Tinosa arrived in Pearl Harbor, her 16th torpedo was given a complete inspection. After an all too familiar examination, the torpedo was declared to be in perfect working order. Commander Daspit had received the same report from his chief torpedo man prior to launching more than 10 torpedoes on 90-degree tracks at a stationary target, yet each torpedo had failed to detonate. Was the 16th torpedo an exception? Admiral Lockwood sought to answer this question with the type of common sense test that identified the depth control problem.

Captain C.B. Momsen suggested loading inspected torpedoes, including Tinosa’s 16th, into a submarine, then firing them against the vertical cliffs off the island of Kahoolawe. The first torpedo that failed to detonate would be recovered and carefully dissected for clues. Lockwood agreed and assigned the submarine Muskellunge to the task.

Maneuvering as close to a 90-degree track as possible, the submarine fired three torpedoes against the rock cliffs. The first two exploded, but the third threw up the familiar geyser of compressed air and water. Divers carefully retrieved the activated yet unexploded torpedo. The valuable dud was then hauled back to Pearl Harbor for examination.

The technicians removed the contact mechanism and discovered that the device had correctly released the firing pin, but the pin had not struck the fulminate caps with sufficient force to set them off. Curiously, the stud guides that directed the firing pin into the primer caps were severely bent and deformed. With the weak link apparent, experiments began to focus on the malfunction.

Lockwood’s men replaced the TNT in several warheads with cinder concrete and attached the normal contact mechanism. Test torpedoes were then dropped 90 feet along a wire suspended from a crane into an empty drydock where they landed squarely on steel plates. A direct, 90-degree hit produced a dud seven out of 10 times–a 70 percent failure rate almost two years into the war. By adjusting the target plates to a 45-degree angle, the failure rate was cut in half. At a still greater angle, the exploders worked without fail. Lockwood immediately directed his boats at sea to launch their torpedoes from large, obtuse angles. They were ordered to improvise, to use anything but the textbook 90-degree track.

The internal failures of the contact mechanism can best be understood through the forces at work in a live torpedo. When a 3,000-pound torpedo traveling at 46 knots struck the hull of a ship, incredible forces were unleashed. The initial force of deceleration equaled approximately 500 times the force of gravity. Transferred to the firing pin, this force appeared as friction between the pin and the guides along which it traveled for accuracy. These stud guides were exposed to nearly 190 pounds of pressure from the contact and resulting deceleration. The firing spring was unable to overcome this tremendous friction and pressure with enough force to drive the firing pin successfully into the primer caps. When a torpedo struck a glancing, angled blow, the force of impact was lessened enough to allow the spring to push the pin into the caps, causing detonation.

The solution turned out to be relatively simple. The Pearl Harbor workshops designed and mass-produced modified firing pins from the propeller blades of Japanese aircraft downed in the December 7, 1941, attack. The new pins were made as light as possible in order to reduce the friction on the stud guides. Testing this handiwork, Lockwood ordered the submarine Halibut, armed with modified exploders, to repeat the Kahoolawe tests. Each torpedo was again set to run as close to 90-degrees as possible to fully test the new pins. Six out of seven torpedoes exploded. Although one still failed, it was a significant improvement from a 70 percent failure rate.

During the 1930s, the Bureau of Ordnance had conducted similar tests designed to ensure a reliable contact mechanism in time of war. The Newport Torpedo Station flung torpedoes against steel plates over sand and discovered then that the firing pins failed to strike the caps with sufficient force. Their solution was to increase the strength of the firing spring. The tighter spring seemed to solve the problem, but it did so at the speed of 1930s torpedoes. Torpedo speeds had increased to 46 knots by World War II, and this increase created greater impact forces. The increased speed essentially negated the strengthened spring. If Tinosa’s torpedoes had been set for slower speeds or obtuse angles, Tonan Maru No. 3 would not have escaped. It took almost two years of wartime trials and tribulations, but American submariners were finally equipped with reliable and effective torpedoes.

The Bureau of Ordnance and the Newport Torpedo Station were guilty of designing and issuing an entire generation of faulty torpedoes. Peacetime budget constraints and a preservationist attitude toward ordnance combined to create an interwar regimen under which the vast majority of scientists and submariners who rotated through Newport never heard or saw a torpedo explosion. To compound this error, both organizations proved incapable of making the transition from peacetime apathy to wartime demand and accepting incriminating combat evidence suggesting major ordnance flaws. Their blind faith and anemic testing may have saved money and material before the war, but it certainly cost lives during the war. Because of this logistics fiasco, veteran submariner and historian Paul Schratz said he ‘was only one of many frustrated submariners who thought it a violation of New Mexico scenery to test the A-bomb at Alamagordo when the naval torpedo station was available.’ Legitimate fault for this debacle must be assigned for the sake of those survivors and their fallen comrades who endured the struggle and won the war.

Perhaps Admiral Lockwood encapsulated the submariners’ long frustration best when he suggested at a wartime conference in Washington that, ‘If the Bureau of Ordnance can’t provide us with torpedoes that will hit and explode… then for God’s sake, get the Bureau of Ships to design a boat hook with which we can rip the plates off a target’s side.’ Although his submarines never had to resort to such measures, history has tended to overlook their early months of struggle, focusing instead on the final two years of their campaign.

What must never be forgotten is the fact that just over 50 years ago, submariners were forced to engage the enemy for 18 months with ordnance that proved to be at least 70 percent unreliable. Often, Japanese merchantmen would enter port with unexploded Mark XIV torpedoes thrust into their hulls. Despite the problems with ordnance, American submariners, a mere two percent of U.S. naval personnel, sank more than 1,178 merchant vessels and 214 warships, totalling more than 5,600,000 tons. They sacrificed 52 submarines, 374 officers and 3,131 enlisted men from their close-knit ranks. The Silent Service suffered 40 percent of all naval casualties in the Pacific, yet managed to destroy 55 percent of all Japanese ships. American submarines succeeded where the Germans had twice failed–in the systematic and complete blockade of an island nation.

One can only speculate as to the war’s outcome had there been reliable torpedoes available from the onset. As for the American submarine campaign against Japan, we must always honor its sacrifices, take pride in its accomplishments and continue to learn from its mistakes–mistakes that fostered a scandal described by Clay Blair, Jr., as ‘the worst in the history of any kind of warfare.’

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This article was written by Douglas A Shireman and originally appeared in the February 1998 issue of World War II magazine. For more great articles subscribe to World War II magazine today!

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