[3] After the fixes, the Mark 14 played a major role in the devastating blow U.S. Navy submarines dealt to the Japanese naval and merchant marine forces during the Pacific War.

[13] At Ralph Christie's urging, equatorial tests were later conducted with USS Indianapolis, which fired one hundred trial shots between 10°N and 10°S[14] and collected 7000 readings.

Chief of Naval Operations William V. Pratt offered the hulk of O'Brien-class[16] destroyer Ericsson,[15] but prohibited the use of a live warhead, and insisted the Bureau of Ordnance (commonly called BuOrd) pay the cost of refloating her if she was hit in error.

In 1923, Congress made NTS Newport the sole designer, developer, builder and tester of torpedoes in the United States.

The short supply of Mark 14 torpedoes was compounded by a 10 December 1941 Japanese air raid on Cavite Navy Yard in the Philippines.

The frugal, Depression-era, peacetime testing of both the torpedo and its exploder was woefully inadequate and had not uncovered many serious design problems.

[37] Responsibility lies with the Bureau of Ordnance, which specified an unrealistically rigid magnetic exploder sensitivity setting and oversaw the feeble testing program.

[37] Therefore, additional responsibility must also be assigned to the United States Congress, which cut critical funding to the Navy during the interwar years, and to NTS, which inadequately performed the very few tests made.

Looking back in 1953, the BuOrd speculated, "Many shots planned for impact against the side of a ship missed because of deep running, yet damaged the enemy due to the magnetic influence feature of the Mark 6.

On 24 December 1941, during a war patrol, Commander Tyrell D. Jacobs in Sargo fired eight torpedoes at two different ships with no results.

He pursued the targets for fifty-seven minutes[41] and made certain the TDC bearings matched perfectly before firing two torpedoes at each ship from an average range of 1,000 yd (910 m).

[42] A few days later, he discovered the torpedoes were running too deep, and corrected the problem,[43] Jacobs detected a big, slow tanker.

[44] A similar experience happened to Pete Ferrall in Seadragon, who fired eight torpedoes for only one hit and began to suspect the Mark 14 was faulty.

[45] Shortly after replacing John E. Wilkes as Commander of Southwest Pacific submarines in Fremantle, Western Australia,[46] newly minted Rear Admiral[46] Charles A. Lockwood ordered a historic net test at Frenchman Bay, Albany on 20 June 1942.

On 1 August 1942, BuOrd finally conceded the Mark 14 ran deep, and six weeks later, "that its depth-control mechanism had been 'improperly designed and tested'".

A light exercise head made the torpedo positively buoyant, so it would float to the surface at the end of its run.

[51] Also, the depth mechanism was designed prior to the warhead's explosive charge being increased, making the torpedo even heavier overall.

The depth problem was finally addressed in the last half of 1943 by relocating the sensor point to the midbody of the torpedo where hydrodynamic effects were minimized.

Lieutenant Commander John A. Scott in Tunny on 9 April 1943 found himself in an ideal position to attack aircraft carriers Hiyō, Junyo, and Taiyo.

Much later, intelligence reported each of the seven explosions had been premature;[38] the torpedoes had run true but the magnetic feature had triggered and exploded the warheads too early.

[64] On 10 April 1943, Bureau of Ordnance Chief Admiral Blandy wrote Lockwood that the Mark 14 was likely to explode prematurely at shallow depths.

Earth's magnetic field near NTS, where the trials (limited as they were)[68] were conducted, differed from the areas where the fighting was taking place.

[73] Nonetheless, Lockwood waited to see if Bureau of Ordnance commander Admiral William "Spike" Blandy might yet find a fix for the problem.

[75] In late June 1943, Rear Admiral Lockwood (by then COMSUBPAC) asked Commander-in-Chief of the Pacific Fleet (CINCPAC) Chester Nimitz for permission to deactivate the magnetic exploders.

If a torpedo was still turning to get on course or had not stabilized its depth when the warhead armed, the exploder could see a magnetic field change and detonate.

The contact pistol appeared to be malfunctioning, though the conclusion was anything but clear until running depth and magnetic exploder problems were solved.

[84] Daspit, suspicious by now he was working with a faulty production run of Mark 14s, saved his last remaining torpedo to be analyzed by experts back at base.

[38] Daspit's cruise raised enough of an issue that tests were carried out by COMSUBPAC's gunnery and torpedo officer, Art Taylor.

A quick fix was to encourage "glancing" shots[85] (which cut the number of duds in half),[86] until a permanent solution could be found.

Lessons learned allowed surface ships such as destroyers to remedy the failings of the Mark 15; the two designs shared the same strengths and faults.