The torpedoes were fairly close to the surface because I wanted to use the impact pistol. The waters were shallow and I didn't want the torpedoes to hit a sand bar or net. I think the torp depth was only 2 meters. The game renders the wake regardless. In another case I fired off one torpedo at 10-11 meters depth, and the tanker sped off right as the fish was about to hit.
I know what you mean about that training mission. I was able to get that ship after the umpteenth time by programming just a little bit of forward speed into the Torpedo Kommandogerat. That mission is annoyingly difficult because the ships are scattered to the four winds and zig zag as soon as one goes down. I was only able to sink all the ships by going full speed on the surface and using the UZO to aim and fire fast torpedoes from 500 meters.
I didn't imagine that the bug would affect everything in the single missions and campaigns too, and that's a shame.