Construction of the Graf Zeppelin was started in 1936 and construction of an unnamed sister ship was started two years later in 1938, but neither ship was completed. In 1942 conversion of three German passenger ships (Europa, Potsdam, Gneisenau) and two unfinished cruisers, the captured French light cruiser De Grasse and the German heavy cruiser Seydlitz, to auxiliary carriers was begun. In November 1942 the conversion of the passenger ships was stopped because these ships were now seen as too slow for operations with the fleet.