What sub is this and why is it apparently unsinkable/undamagable?
 

http://i.imgur.com/iQuedOX.png

I gave this guy about 8-10 deckgun hits a mix of HE an AP rounds but all it did was appear to slightly fragment and it did not slow down, deviate from course or "act" normal in response, no response at all. Can we fix that or remove these objects from from the campaign?

Really spoils the realism.

U class submarine
 

It's a U class submarine used by UK in the Mediterranean due to it's small size.
Sink him with a torpedo not with deck gun because ha can submerge.
If he spots you he submerge so when you find him go periscope deph and follow him with hydrophone then get yourself in attack position and want him to emerge.Fire a torpedo and hit him. Even if he seems not to sink wait a few moments then check the captain's diary and see if he is dead or check the update in campaign progress.
It's 100% tested!!

Well thats great I hit it several times for certain. This was in the Polish engagement zone. I mistook it for a Polish sub since it was operating in that area. I didnt want to waste a torpedo on it because it didnt look big enough but she was unsinkable as Molly Brown from DG fire.

It is a Polish sub (in game) - one of 5 patrolling that bay

Some subs have indestructible con towers - aim for hull or use torps
Sorry for the realism being spoilt:arrgh!:

It is what it is. :( lol