I found this interesting technical article on why US torpedo's didn't work in the first two years of the war.
U.S. Navy Torpedoes (part two)
US NAVY TORPEDOES
by Frederick J Milford
Part Two: The great torpedo scandal, 1941-43
Reproduced with permission from the October 1996 issue of THE SUBMARINE REVIEW,
a quarterly publication of the Naval Submarine League, P.O. Box 1146, Annandale, VA 2200
Naval rearmament, which began in the mid-1930s, and WW II had dramatic impact on US torpedo programs. Three of the most significant changes were the enormously increased requirement for torpedoes, the urgent need for new torpedo types and the first use of US torpedoes against enemy vessels. The increased requirement was satisfied by expanding government facilities, the Newport Torpedo Station (NTS-Newport) was enlarged, the Alexandria Torpedo Station was reopened1 and Keyport Torpedo Station began assembling torpedoes, and by initiating civilian production. Total production between 1939 and 1945, almost 60,000 torpedoes, was about equally divided between the torpedo stations and contractors. Mk.14 torpedoes were, however, in such short supply in 1942 that some fleet boats loaded out with Mk.10 torpedoes or even Mk.15s in the after tubes2. New types of torpedoes are discussed in Part Three of this series. Firing warshots was an almost totally new experience for the US Navy. It seems probable that the number of warshots fired against enemy vessels in December 1941 was larger than the total number of warshot torpedoes fired for any purpose3 in the entire past history of the US Navy. Perhaps not surprisingly, this intensive use of torpedoes revealed shortcomings that had been previously obscured, especially in the new service torpedoes and particularly in the Mk.14.
1 The Newport monopoly on the torpedo business had a significant effect on the development of torpedoes. The extent of the monopoly and efforts to preserve it are illustrated by opposition to the reopening of Alexandria, which was accomplished in the face of demands from New England politicians and labor leaders that Newport be expanded. Resuming torpedo work at Alexandria expeditiously was possible only because when it was closed in 1923 it had been incorporated into the Washington Navy Yard. Consequently, the torpedo station could be reopened without an Act of Congress.
2 This was mentioned by Adm. B.A. Clarey in a recent interview with John DeVirgilio and confirmed by RAdm M.H. Rindskopf who also supplied key parts of the following material. Mk.15 torpedoes were too long to be loaded through hatches or stowed in the torpedo rooms. They were also too long for either the forward or longer aft torpedo tubes. They were modified, probably by using shorter warheads, and loaded into the aft tubes through the muzzle doors. USS Drum, SS-228, sailed so loaded on her second war patrol from Pearl Harbor in July 1942. All four Mk.15s were fired.
3 This, of course, means self propelled torpedoes and excludes spar and towed devices. Apparently, only eleven torpedoes fired by US forces against enemy vessels prior to WW II (AL boats against U-boats). The number of warheads used in training and test and evaluation was very small. US submarines made 54 war patrols in December 1941 and fired 66 torpedoes at enemy targets, quite possibly more warheads than had been fired in the entire previous history of the US Navy.
The trio of new service torpedoes, Mk.13, Mk.14 and Mk.15, which represented the bulk of the US Navy torpedo development in the 1930's were on the one hand excellent weapons and had long service lives, Mk.13 remained in service until 1950, the Mk.14 was a valuable service weapon until 1980 and Mk.15 served as long as twenty-one inch torpedoes remained on destroyers. On the other hand they all had significant problems that were only fixed after wartime use began. The Mk.14, which was the principal submarine weapon, was plagued with defects that vitiated its use as a weapon until mid-1943. The conflict between the shore establishment and the operating forces over these problems was a very significant and much discussed factor in US submarine operations during WW II.
THE GREAT TORPEDO SCANDAL
The Great Torpedo Scandal4 emerged and peaked between December 1941 and August 1943, but some of its roots went back twenty five years. It involved primarily the Mk.145 and three distinct problems, depth control, the magnetic influence exploder6 and the contact exploder, whose effects collectively eroded the performance of the torpedoes. The scandal was not that there were problems in what was then a relatively new weapon, but rather the refusal by the ordnance establishment to verify the problems quickly and make appropriate alterations. The fact that after twenty five years of service the Mk.10 had newly discovered depth control problems adds weight to the characterization of the collection of problems and responses as a scandal. These comments should, however, be mitigated a little by the fact that each of the Mk.14 problems obscured the next. Although BuOrd did not identify the final problem, contact exploder malfunction when a torpedo running at high speed struck the target at ninety degrees, their response, once the difficulty had been identified, was notably prompt. In spite of the promptness of BuOrd's response, by the time it reached Pearl Harbor a number of relatively simple solutions to the problem had been proposed, and modifications had already been designed and implemented. This was, however, almost two years after the United States entered WW II.
4 At least three MA theses have been written about the problems of the Mk.14 torpedo (Ingram (197, Shireman (1991) and Hoerl (1991)); the problem was noted by Morison and is discussed at length in Theodore Roscoe, , _United States Submarine Operations in World War II_, Annapolis: Naval Institute Press, 1949; Clay Blair, Jr., "Silent Victory: The U.S.Submarine War Against Japan", Philadelphia and New York: J.B.Lippincott, 1975; and Edwyn Gray, "The Devil's Device: Robert Whitehead and the History of the Torpedo" (Revised Edition), Annapolis, USNI Press, 1991.. David E. Cohen has written a paper on the subject, "The Mk.XIV Torpedo: Lessons for Today", Naval History, Vol.6, No.4, Winter 1992, pp.34-36"
5 Criticism of the destroyer launched Mk.15 is almost nonexistent. This is strange because the principal differences between the Mk.14 and the Mk.15 were in the size of the warhead, the fuel load, three speed vice two speed and slightly slower high speed, 45.0 k vice 46.3 k. One might speculate that it is even more difficult to distinguish misses from duds in a high speed destroyer attack than it is in a more measured submarine attack. The Mk.15 did, in fact suffer from the same defects and they were rectified in essentially the same way that those of the Mk.14 were. The Mk.13 was a slower speed torpedo so it did not have the contact exploder problem and it used the Mk.4 exploder which did not have the magnetic influence feature.
6 Properly, the exploder is the entire Mk.6 assembly. It has an influence feature and a contact feature. This leads to awkward verbiage so we refer to the magnetic influence exploder and the contact exploder. Both are parts of the Exploder Mk.6, which weighs approximately 90 lbs, and some elements of the exploder function in both modes. The exploder also contains important safety features.