U-556 was a German Type VIIC submarine in World War II, commanded by Kapitänleutnant Herbert Wohlfarth.
It was connected in a sponsorship with the Bismarck. Kapitänleutnant Wohlfarth had sworn to Kapitän Lindemann before Neptune to stand by the battleship in any situation.
Ironically, this submarine could have actually changed the fate of the Bismarck. On the eve of the final battle, it sighted the aircraft carrier Ark Royal, just as the Swordfish torpedo bombers were taking off to seal the Bismarck’s fate. However, since the submarine had no torpedoes left on board, it was unable to attack and could only listen as its “big brother” met its end.