The Seydlitz was laid down in 1936 as a slightly modified version of the Admiral Hipper heavy cruiser class. The heavy cruiser Seydlitz was a slightly modified version of the Prinz Eugen and the Prinz Eugen was a slightly modified version of the heavy cruiser Admiral Hipper. Laid down as cruiser K and assigned a builders number of 940, the Seydlitz was launched on 19 January, 1939.

In the fall of 1939 the Soviet Union expressed interest in purchasing the still incomplete Seydlitz but the German government declined. Instead, Germany agreed to sell Seydlitz's sistership, the Lützow, to the Soviet Union while continuing work on the Seydlitz. With the start of the war, Germany redirected more resources into u-boats and destroyers which could be more quickly produced and have an immediate impact on the war. The Seydlitz languished and work proceeded very slowly.

In the summer of 1942, with the battle of the Atlantic turning against Germany, the Navy high command decided to convert the Seydlitz to an aircraft carrier as they recognized an aerial component to the naval war was necessary. Plans were drawn up for converting the vessel into the aircraft carrier Weser I. Work on the conversion was immediately began but by January 1943, with materials becoming scare, the conversion process stopped. Abandoned, the Seydlitz rested at the dockside for two years until she was scuttled on 29 January 1945 so the vessel wouldn't fall into the hands of the approaching Russians. In 1946 the Russians raised the Seydlitz and eventually scrapped the ship sometime in the 1950s.