Though laid down and launched before the start of the war, the Graf Zeppelin was never completed or commissioned, and it never saw action.
Whilst four aircraft carriers of the class had originally been planned, constant in-fighting between the Kriegsmarine and Luftwaffe, as well as a priority on the building of U-Boats hampered their construction, with the planned four carriers quickly reduced to two. Construction on the ship that would eventually be christened Graf Zeppelin was eventually halted in 1940.
However, with the role of the carrier proving itself in the Battle of Taranto, in the sinking of the Bismarck and at Pearl Harbour and Midway prompted construction to briefly continue. The Graf Zeppelin was almost completed in 1943 but Hitler, disappointed with the Kriegsmarine, halted all surface fleet construction. The Carrier was captured by the Soviet Union at the end of the war, and was sunk as a target ship in 1947.
Though obviously never seeing action in reality, Kriegsmarine players are afforded new tactical options in Victory at Sea with the opportunity to include this carrier in their fleet.