U.S. WW2 torpedoes

Early in the Second World War, especially World War Two in the Pacific, there were severe effectiveness problems with United States Navy torpedoes. Eventually, the engineering problems were corrected, although the Japanese Long Lance torpedo remained the most effective heavyweight torpedo of the war.

Early failures
It must be understood that, for the time, a torpedo, especially those used by submarines and torpedo bombers, was extremely high technology and extremely expensive. They were developed by the Navy's Bureau of Ordnance, and were poorly tested before being deployed. The Bureau insisted that operational failures had to be the fault of the fleet; the design was flawless.

It may well have been that the dismal performance of Navy's initial torpedo bomber, the TBD Devastator, may have been partially due to the Mark XIII air-dropped torpedo, not exclusively the limitations of the aircraft or the tactics used in torpedo tactics. At the Battle of Midway, 37 of 41 TBDs sent against the Japanese carrier force failed to return, and there were no hits by U.S. torpedoes. It is unlikely there was a single cause for the lack of success, but, in a variety of operations, Mark XIII torpedoes were observed to have hit a target but not exploded.

"Submariners were having the same problems with the Mark XIV Field ordinance men attempted to modify the weapon until the Navy Bureau of Ordinance in Washington sent a direct order forbidding any modifications and assuring everyone the Mk XIII torpedo was faultless...It seems the carrier groups took it at face value and looked for solutions in the maintenance and delivery of the weapon." Submariners persisted in investigating the Mark XIV, and found several serious problems.

Depth setting
"The torpedoes had been tested with dummy warheads, that is, the space for the warhead had been filled with water when the torpedo was tested. No one apparently thought to ask how heavy the actual warhead would be, and the cost of the torpedoes entered the picture as a reason to curtail further testing of the torpedo. Due to the difference in weight of the dummy warhead and the actual warhead, the torpedo ran eleven to 14 feet below set depth."

Fuze problems
The depth problem was compounded by problems in the complex fuzing system of the torpedoes: an impact fuze, and a magnetic influence fuze. There were multiple problems with the impact fuze: it would work only when striking the target within a much narrower geometry than had been planned. Both the horizontal angle at which the torpedo hit the target ship, and the vertical slope of the ship's hull, affected the engagement geometry.

Even when the geometry was perfect, there were mechanical problems inside the fuze. Too hard an impact would deform the linkage between the impact sensor and the detonator, causing a failure to detonate.

The magnetic influence fuze was essentially too far beyond the non-electronic technology in use. Had it worked, the depth setting problem might not have been an issue, since this exploder was intended to detonate the torpedo's warhead at the ship's most vulnerable point: under its keel. Simply stated, the magnetic fuze almost never worked, and was eventually disabled, with the focus of corrective action on the impact subsystem.