thanks for the tips.
Last night I picked up a contact NW of Loch Ewe , I surfaced and opened the engines up and repeated again after a while to check which direction it had travelled.
a while later I had succesfully intercepted a town-class warship with an a&b some distance behind it.
I lined myself up and waited until the town class came right across me .
I sunk him with one torp hit
I couldnt get a decent line on the A&B , so I dived and evaded him.