I share you pain with the Mk-14s. Now I know why they are designated Mk-14. That is the rough percentage of torpedoes that won't be a dud [14%]
I hear that is you shoot at slow speed that it helps but frankly I have not found that to be true. I am also in 1943 and I find that I have to shoot 6 fish to get two booms (contact only shallow depth).
I get about 50-60% dud rate.
It is very very frustrating.