I'm sitting mid to late 1940, VIIB, 54% realizm (I think, haven't had the chance to play for three weeks now but it's constantly on the stages of my mind).
You could say I cheat, or at least I know in the real world they didn't put an eel into a merchant then surface and finish it off with the deck gun. Anything under 4k I hit only with the deck gun. So if I remember correctly, I'm at roughly 140k tonnage with 4 eels left and probably not enough fuel to return home afterwards.
I'll have to run slow until the batteries are charged, then run at 30m until the air or batteries are depleted, then recharge and go again. Does anyone have a great way of getting from the western approaches back to Wilmshaven on fumes?
Don't answer that, I'm not going to hijack this thread.