In one of the first patrols of my curent career, still on Type II, I hit 2000t Small Merchant with one torpedo. She stoped, listed to port but didn't sink. I fired a coup de grace, but she was still afloat.

Reluctant to fire my last torpedo, I surfaced and used my flak gun

. I spent all the ammo (some 800 rounds), but didn't sink her.
Finaly I fired my last torpedo, sank her and return home with some 5000 t.