Seydlitz was a heavy cruiser of the German Kriegsmarine, fourth in the Admiral Hipper class, but was never completed. The ship was laid down in December 1936 and launched in January 1939. In March 1942, the Kriegsmarine decided to pursue aircraft carriers over surface combatants. Seydlitz was among the vessels chosen for conversion into auxiliary aircraft carriers. The ship was to have had a complement of ten Bf 109 fighters and ten Ju 87 divebombers.