U-523 collided with the battlecruiser 'Scharnhorst' in August 1942 (or rather the other way round - Kapitan zur See Huffmeier, the then commander of the 'Scharnhorst', had a reputation for what might be charitably called misfortunes) during maneouvers in the Baltic. 'Scharnhorst' had to go into dry dock for repairs, but U-523 survived; I imagine the battlecruiser did a bit more than scratch the U-boat's paintwork though!