Soviet submarine K-21 is a K-class submarine of the Soviet Navy during World War II.

Tirpitz was the second of two Bismarck-class battleships built for Nazi Germany's Kriegsmarine (navy) prior to and during the Second World War. Named after Grand Admiral Alfred von Tirpitz, the architect of the Kaiserliche Marine, the ship was laid down at the Kriegsmarinewerft in Wilhelmshaven in November 1936 and her hull was launched two and a half years later. Work was completed in February 1941, when she was commissioned into the German fleet. Like her sister ship, Bismarck, Tirpitz was armed with a main battery of eight 38-centimetre (15 in) guns in four twin turrets. After a series of wartime modifications she was 2000 tonnes heavier than Bismarck, making her the heaviest battleship ever built by a European navy.