British S-Boats... Unsinkable?

[Thomen]

Hi all! =)

I was on my way back to Wilhemshafen when my look-out spotted a surfaced sub. We maneuvered into firing position at his stern and after IDing it as a British S-Class submarine we opened up on him. The firefight so far lasted for around 30 minutes. The enemy is dead in the water, lost it's weaponry.
He got hit by ca 40 8.8cm shells and 120 3.7cm rounds, plus 2 torpedo hits. And his is still refusing to sink! I rammed him right in front of his conning tower... no effect.

My boat, after slapping patching on the holes he shot into me, and fixing the equipment, is running low on ammunition. I got 2 heavily wounded men on board and hull integrety is down to 60%.

Anyone has any idea whats going here? hehe