Mid way through WW2 the British Admirality ordered its destroyer captains to try to avoid ramming attacks on subs since it always resulted in a destroyer needing its bows repaired. Potentially a destroyer could cripple itself if it rode over a sub completely and damaged its prop shafts. Read the account of one escort captain once. He mentioned seeing this happen once and seeing the destroyer get torpedoed while still crippled. Back on the subject of battleships HMS Dreadnought is the only battleship to have sunk an enemy sub. Quite a few battleships have accidently sunk friendly subs. The Sub sunk in the second battle of Navik wasn't sunk by HMS Warspite as Tiornu suggested but a Swordfish floatplane launch from Warspite. Ram bows for some reason hung on for an insanely long time but eventually people realised they were useless in war time and dangerous in peace time.