Without knowing a huge amount about WW2 warships, I would put forth the convoy escort vessels that escorted the Russian convoys. That would have to be one of the worst jobs of WW2, in the worst weather, there mission of getting supplies through to Russia was essential to the war effort. When radar technology became readily available and the enigma codes were cracked they really had the German U-Boat force (essential to Germany's success in the war) on the back foot.