Starting in the mid-1930s, the "Reichsmarine" began design studies for a new type of aircraft carrier to meet the requirements of the revitalized German fleet; by 1936, these concepts had developed into the , the first member of which was laid down for the renamed "Kriegsmarine" in December of that year. A second vessel, designated "Flugzeugträger" B, followed in 1938, and the Plan Z naval expansion plan envisioned a further two carriers of a new design to be in service by 1945. Despite this, neither of the "Graf Zeppelin"-class ships would be completed due to the outbreak of World War II in September 1939; work was halted on both in early 1940, and "Flugzeugträger" B was scrapped shortly thereafter. Work on "Graf Zeppelin" recommenced in 1942, but was again stopped in early 1943 due to more pressing requirements. During this second period of construction, the "Kriegsmarine" proposed to convert several passenger ships and two unfinished cruisers into auxiliary aircraft carriers, though none of these were completed either, and by 1945 all had either been sunk or seized as war prizes by the Allied powers.