The Magnetic Exploder Problem

The problems with the Mark 6 exploder concerned the submarine crew more than the problems of deep running torpedoes for they caused either a premature detonation or a dud, either of which caught the attention of the targeted vessel with reprisals sure to follow. Especially irritating were the torpedoes that detonated as soon as they encountered the slightest deviation in the magnetic field around them, which was, in some cases, just a few yards from the torpedo tube.

Too often, when the torpedo was set to run deep and pass under the keel in order to have the magnetic influence exploder detonate the warhead, nothing would happen. But when the torpedo was set at a shallow depth to have the back up contact exploder detonate, the magnetic influence exploder would detonate the warhead prematurely (if it chose to work at all). When the Mark 6 detonated the warhead prematurely it was sometimes mistaken by the submarine commander for a hit or sinking. At least it looked like a hit through the periscope, and so would be reported as such.

The Mark 6 Exploder was considered extremely complex by many people, with a flawless unit only a far off pipe dream. Three separate explosive actions were required to detonate the warhead in the torpedo. In the first action a firing pin struck a primer cap, which in turn set off a detonator in the base of the booster charge, finally the shock wave from the booster detonated the TNT (or Torpex). One of the mechanisms that activated the firing pin received its signal by sensing the earth’s magnetic field, the magnetic influence component of the Mark 6 Exploder.

The magnetic field under a ship was presumed to be a hemisphere and a torpedo set at the proper depth would intersect this field at its lowest point, directly under the keel. But the magnetic field may have been much more flattened than originally presumed, resembling a thick disk. The torpedo would then encounter the strong magnetic field from this disk at some distance from the hull and detonate the warhead before the torpedo was under the keel. Unless the exploder was perfectly adjusted, it would activate at distances from 50 feet to 150 feet from the hull. It appears that these premature detonations were more prevalent when attacking larger targets, such as aircraft carriers, where the warhead would encounter the necessary activating flux density while still some distance from the keel. In other words, the thing was just too hypersensitive and the Fleet began to seriously distrust the Mark 14 Torpedo.

There is another possible explanation. The passive feature of the exploder relied on the target’s magnetic signature and was fooled by local changes in the earth’s magnetic field. Its only test was conducted in Narragansett Bay which has considerably different magnetic conditions than the Pacific Ocean.

BuOrd did not believe any of this and insisted that nothing could be wrong with its creation, until the problem erupted into a major scandal. The operating forces were initially told not to disable the exploder, nor to conduct tests on it. It turned out that the greatest debate between the submarine force and BuOrd was over the Mark 6 magnetic influence exploder. Other than deactivating the magnetic influence feature, no solution to this problem made its way into the Pacific theater during the war.

Instead of being a device which could reduce the number of torpedoes fired against a target, the real effect was an excessive use of the Mark 14 in order to get an explosion at the target (making a weapon already in short supply even scarcer).

More Mark 14 Torpedo

The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 1 [# 120]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 2 [# 121]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 3 [# 122]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 4 [# 123]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 5 [# 124]