Mark 6 exploder

The Mark VI exploder was a United States Navy torpedo exploder developed in the 1920s. It was the standard exploder of the Navy's Mark XIV torpedo.

Development


The Mark XIV torpedo was designed at the Newport Torpedo Station (NTS), Newport, to replace the Mark X which had been in service since World War I. Its fairly small 643 lb warhead required it to explode beneath the keel where there was no armor.

This led to the creation of the sophisticated new Mark VI exploder, to have a magnetic influence feature similar to the British Duplex and German models, all inspired by German magnetic mines of World War I. The Mark VI was intended to fire the warhead some distance below the ship, creating a huge gas bubble which would cause the keel to fail catastrophically.

The Mark VI exploder, designated Project G53, was developed "behind the tightest veil of secrecy the Navy had ever created." Small quantities were produced in extreme secrecy, and at a cost of US$1,000 per unit, by General Electric in Schenectady. The exploder was tested at the Newport lab and in a small field test aboard USS Raleigh. At the urging of the Mark XIV's designer, Lt. Ralph W. Christie, equatorial tests were later conducted with Indianapolis, which fired one hundred trial shots between 10°N and 10°S and collected 7000 readings.

Inexplicably, no live fire trial of the torpedo or exploder was ever done. Chief of Naval Operations William V. Pratt offered the hulk of Cassin-class destroyer Ericsson, 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. These were strange restrictions, as Ericsson was due to be scrapped. BuOrd declined. A service manual for the exploder "was written—but, for security reasons, not printed—and locked in a safe."

Problems
After the Mark XIV entered combat service in the Pacific War, it was discovered the torpedo had several major flaws.
 * It tended to run about 10 ft deeper than set.
 * The magnetic exploder often caused premature firing.
 * The contact exploder often failed to fire the warhead.

Similar problems also plagued the Mark XV torpedo used by U.S. Navy destroyers. That all of these problems could lead to misses or failures, they tended to mask on another, making isolating any of them harder.

Premature explosions
Many submarine commanders in the first two years of the war reported explosions of the warhead with little to no damage of the enemy. The magnetic exploders were triggering prematurely, before getting close enough to the vessel to destroy it. Earth's magnetic field near NTS, where the trials (limited as they were) were conducted, differed from the areas where the fighting was taking place.

Duds
Early reports of torpedo action included some dud hits, heard as a dull clang. In a few instances, Mark 14s would strike a Japanese ship and lodge in its hull without exploding. The contact pistol appeared to be malfunctioning, though the conclusion was anything but clear until running depth and magnetic exploder problems were solved. Daspit's experience was exactly the sort of live-fire trial BuOrd had been prevented from doing in peacetime. It was now clear to all at Pearl Harbor the contact pistol was also defective.

Solutions
Against orders, some submariners disabled the magnetic influence feature of the Mark VI exploder, suspecting it was faulty. An increase in hits was reported. Shortly after replacing Wilkes in Fremantle, newly minted Rear Admiral Charles Lockwood ordered a historic net test at Frenchman Bay on 20 June 1942. Eight hundred Mark XIVs had already been fired in combat.

After a historic net test by Jim Coe's Skipjack, BuOrd on 1 August 1942 finally conceded the Mark XIV ran deep, and six weeks later, "that its depth-control mechanism had been 'improperly designed and tested'". This satisfied Lockwood and Robert H. English (then COMSUBPAC ), who refused to believe the exploder could also be defective.

Finally, in July 1943, Admiral Lockwood ordered his boats to deactivate the Mark VI's influence feature and use only its contact pistol.

Tests were carried out by COMSUBPAC 's gunnery and torpedo officer, Art Taylor (ex-Haddock). Taylor, "Swede" Momsen, and others fired warshots from Muskallunge into the cliffs of Kahoolawe, beginning 31 August. Their third test shot was a dud. This revealed the firing pin had not been able to contact the detonator hard enough to fire the warhead.

To avoid "shaking hands with St. Peter" (as Lockwood put it), E.A. Johnson, USNR, supervised by Taylor, dropped dummy warheads filled with sand from a cherry picker raised to a height of 90 ft. In 7 out of 10 of these trials, firing mechanisms bent, jammed, and failed with the high inertia of a straight-on hit (the prewar ideal). A quick fix was to encourage "glancing" shots (which cut the number of duds in half), until a permanent solution could be found. Lightweight aluminum alloy (from propellers of Japanese planes shot down during the attack on Pearl Harbor) was machined to take the place of the Mark VI's heavy pin block so inertial forces would be lower. Electrical switches, developed by Johnson, were tried as well. Both fixes worked and were relatively easy to implement. In September 1943, the first torpedoes with new contact pistols were sent to war. "After twenty-one months of war, the three major defects of the Mark 14 torpedo had at last been isolated. ... Each defect had been discovered and fixed in the field—always over the stubborn opposition of the Bureau of Ordnance."