external reserve torpedos

[Mittelwaechter]

Well, Herr Kaleun, it's your decision to load externals at 15 m/s or not.
Don't let you be ruled by the game, Sir!

Simply follow your own rules:
external reload only at 3 m/s or lower;
man the deckgun to load the externals - at least two torpedo qualified;
first half of the reloading time: under attack stay surfaced for three minutes; keep the deckgun manned; shoot the torpedo later to simulate its loss.
second half of the reloading time: don't dive at all; get your crew in after three minutes or let them work to enable your dive

No need to be enforced by the game!