It was '40, so radar was impossible.
Guess I just got bad luck. Anyway, how the story ended: one of the escorts saw me, and shells came flying over my head. We went to 100m below (after taking a hit, but nothing serious) and tried to avoid the DC's. No luck tough, got hit twice, the first wasn't that bad, but it took out my periscopes, so the mission was allready over. The second however sent me straight to Davy Jones' Locker, without even a bit of deathstruggle or agony in between...
Guess I've been a bit too long out of the game...