I went to periscope depth, fired all four tubes at the target. The bells started ringing from the torpedo salvo launched from the sub following me. So i dived back down to 25m waited fr the enemy torps to pass over me and then returning to periscope depth to launch the next salvo.
After hitting him with torps, torps, torps and a side order of torps, (aswell as the odd torp from the sub following me that overshot and hit the BC). I eventually had the great satisfaction of watching the BC begin to sink! I then started diving with it and following it to crush depth.