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.

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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.

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