The primary problem with German torpedos was the same as one of the USN's major
problems with torpedoes’ in WWII -- magnetic exploders.
The magnetic influence exploder was the high-tech wonder device of the 1930's.
The theory was excellent; instead of relying on a contact explosion (in which
much of the warhead's energy was "wasted" by radiating away from the target or
directly into it on a small area) the influence exploder would allow torpedoes
to run under a ship and explode, making a much more effective use of the
resultant energy against the ship's hull (water, being effectively
incompressible, is a tremendously effective medium for the transfer of
force.) Since warhead efficiency was thus greatly magnified, warhead weight
could subsequently be reduced -- this allowed more weight/space for more
powerful engines, more fuel, etc. So, in theory, the magnetic exploder not
only made a torpedo more lethal, but also increased its performance
capabilities over conventional detonator equipped torpedoes.
However, there was a big gap between theory and operational reality. Local
variations in the magnetic field greatly affected performance, and the
interactions between a ship, its magnetic field, the ocean, weather, the
earth, etc., were very poorly understood. The dynamics of the earth's
magnetic field were largely unknowns. All of these variables made a huge
difference in actual performance, and in service the early mag detonators were
terribly unreliable. In the USN the magnetic exploder saw VERY limited prewar
testing and *not one live shot* against a realistic test target. The device
was so top secret and expensive that few were made and they were withheld from
fleet deployment -- no sub crews had any operational knowledge of them at all
when the war started and the Navy released them for combat. Both the USN and
German ordnance bureaucracy proved extremely slow and resistant to
investigation or changes, and instead tended to blame the problems on poor
marksmanship, bad maintenance, etc.
The Germans had considerable trouble with their magnetic exploders, and
literally lost hundreds, perhaps even more than a thousand, potential kills.
The Americans not only had trouble with the magnetic exploder, but their
conventional impact detonators also had serious problems that were not
effectively dealt with until well into 1943. As a result the USN lost
hundreds of possible kills during the first half of the war.
