Other factors that skew the data. In the Norwegian campaign the German dud rate was near 90% for magnetic variation in shallow water. Early in the war US policy called for submerged sound attacks without periscope observation. It was not the Skipper choice that determined his effectivness. Early in 1943 the USN used a 4 torpedoe spread as the standard attack on merchant ships. The US policy also called for the first torp to be fired ahead as a probable miss, unless the target spotted the periscope and speeded up (or the skipper underestimated speed to begin with) While the Germans varied their salvos Depending on the individual skipper's opinion of the target value and his ability to hit. Kretchmer swore by one torp per ship and clean up with gunfire after the escorts were gone. You will never know how many of the FAT and Sound king torps exploded on the first pass hit dud and how many exploded after the reattack. The fire control on a US S-boat was not close to the TDC. More considerations available if you want such after the election.