from Wikipedia

Graf Zeppelin, Germany's only aircraft carrier during World War II, was named in honor of Graf (Count) Ferdinand von Zeppelin. Its construction was ordered on November 16, 1935, and its keel was laid down December 28, 1936 by Deutsche Werke of Kiel. It was launched on December 8, 1938, but was never completed.
In 1935, Adolf Hitler announced that Germany would construct aircraft carriers to strengthen the Kriegsmarine. The keels of two were laid down the next year. Two years later, Grand Admiral Erich Raeder presented an ambitious shipbuilding program called Plan Z, in which four carriers were to be built by 1945. In 1939, he revised the plan, reducing the number to two. The first German carrier, laid down as "Flugzeugträger A" ("Aircraft carrier A"), was named Graf Zeppelin when launched in 1938. The second carrier — never launched — bore only the title "Flugzeugträger B", but might, if completed, have been called Peter Strasser.

A review of Hitler's conferences on matters dealing with the German Navy, the minutes of which were captured after the fall of the Third Reich, reveals his decreasing interest in the carriers. Marshal Hermann Göring was resentful of any incursion on his authority as head of the country's air power, and he frustrated Raeder at every opportunity. Within his own service, Raeder found opposition in Admiral Karl Dönitz.
By May 1941, Raeder was still optimistic about the project and informed Hitler that Graf Zeppelin, then about 85% complete, would be completed in about a year and that another year would be required for sea trials and flight training. Though Raeder continued to assure Hitler that the carriers would be built, the Admiral's battles with Göring became increasingly bitter. Göring showed his contempt for the naval air arm by informing Hitler and Raeder that the aircraft ordered for Graf Zeppelin could not be available until the end of 1944. Göring's delaying tactics worked.
Construction on the carriers had been fitful from the start. "Flugzeugträger B" was abandoned in 1940 and broken up. Worker and material shortages plagued the Graf Zeppelin. Prodded by Raeder, Hitler ordered Göring to produce aircraft for the carrier and under this pressure, the air marshal offered redesigned versions of the Junkers Ju 87B and the Messerschmitt Bf 109E-3, which were at that time being phased out of the Luftwaffe first-line squadrons. Raeder was unhappy, but he had to accept them or none at all (including, Göring's demand, that the pilots would remain under Luftwaffe command). All this forced another delay in the construction of the carrier: the flight deck installations had to be changed. Later in 1942 projects for naval aircraft included the Me 155 V2 and JU 87E (navalised D version). None of the JU-87E were completed.

By 1943, Hitler had become disenchanted with his Navy. Raeder was relieved at his own request and Dönitz, the submarine admiral, took the top naval post. Work on the then over 95% completed carrier stopped completely. All armaments were removed and transferred to coastal batteries in Norway.
As the end of the war neared, the roughly completed carrier was scuttled in shallow water at Stettin (now Szczecin) on April 25, 1945, just before the Red Army captured the city.
The carrier's history and fate after Germany's surrender was unclear for decades after the war. According to the terms of the Allied Tripartite Commission, a "Category C" ship (damaged or scuttled) should have been destroyed or sunk in deep water by August 15, 1946. Instead, the Soviets decided to repair the damaged ship. It was refloated in March 1946. The last known photo of the carrier shows it leaving Świnoujście (up to 1945 Swinemünde) on April 7, 1947. The photo appears to show the carrier deck loaded with various containers, boxes and construction elements.
For many years no other information about the ship's fate was available. There was some speculation that it was very unlikely that the hull made it to Leningrad, as it was argued that the arrival of such a large and unusual vessel would have been noticed by Western intelligence. This seemed to imply that the hull was lost at sea during transfer between Świnoujście and Leningrad. One account concluded that it struck a mine north of Rügen on August 15, 1947, but Rügen, west of Świnoujście, is not on the sailing route to Leningrad. Further north, in the Gulf of Finland, a heavily-mined area difficult for Western observers to monitor, seemed more likely.
After the opening of the Soviet archives, new light was shed on the mystery. It appears that the carrier was towed to Leningrad. There, after unloading, it was designated as "PO-101" (Floating Base Number 101). The Russians hoped that the carrier could be repaired in Leningrad's shipyards (those in Szczecin were destroyed). When this proved impractical, the ship was towed out to sea, back to the Polish coast. There, on August 16, 1947, it was used as a practice target for Soviet ships and aircraft. Allegedly, the Soviets installed aerial bombs on the flight deck, in hangars and even inside the funnels (to simulate a load of combat munitions), and then dropped bombs from aircraft, fired shells, and shot torpedoes into it. This assault would both comply with the Tripartite mandate (albeit late) and provide the Soviets with experience in sinking an aircraft carrier. By this point, the Cold War was underway, and the Soviets were well aware of the large numbers and central importance of aircraft carriers in the U.S. Navy. Hence, experience in sinking carriers by aircraft was much more valuable in 1947 than before 1945. After being hit by 24 bombs and projectiles, the ship did not sink and had to be finished off by 2 torpedoes. The exact position of the wreck was unknown for decades.
On July 12, 2006 a ship belonging to the Polish oil company Petrobaltic found a 265 m long wreck close to the port of Łeba (a BBC report says 55 km north of Władysławowo) which they thought was most likely Graf Zeppelin. On July 26, 2006 the crew of the Polish Navy's survey ship ORP Arctowski commenced penetration of the wreckage to confirm its identity, and the following day the Polish Navy confirmed that the wreckage was indeed that of Graf Zeppelin. She rests at more than 86 - 87 meters (264 feet) below the surface.

Very interesting article. The major thing to remember about the Graf Zeppelin is that the Germans had absolutely no experience with carrier operations. Even if, and of course this is a big if, she had been completed in time for the war, there were major items standing in the way of her being an effective naval unit. Of course there is the matter of her planes. The 109 and 87 were decent land planes but neither was built from the ground up to be carrier born. That's not to say they couldn't have been good aircraft, but the odds were against them. Then there was the training involved, not just for the pilots, but also the service crews. America, Britain, and Japan had had twenty or so years developing carrier operational experience. They made plenty of mistakes over that time, and learned from them. Germany was trying to develop a carrier, develop aircraft, train the aircrew, train the service crews, develop carrier tactics, all with just one carrier. Not to mention the animosity of Goering and his not wanting to give up any of his precious aircraft. To use an analogy it would have been like the Americans having to come up with the Enterprise, CV-6, without any of the experience gained from Langley, Lexington, and Ranger, and assuming the Air Force had already been a separate agency and didn't like the idea. All this during a war against the largest, or at least second largest, navy in the world, that themselves had plenty of carrier experience.

With all of the above said the Zeppelin wasn't all that good of a design. Can you believe that until a planned redesign in 1942 that added bulges to her she would have listed about 4.5 degrees when fully loaded due to miscalculations? Her armor was built to the same level as a heavy cruiser, but was that really necessary? She was supposed to be able to carry about 42 aircraft, but would have been plenty cramped to operate them. Finally her machinery was based on that of the German heavy cruisers, which proved to be very unreliable in action. Imagine getting out into the North Atlantic then having an engine breakdown?

The Graf Zeppelin stirs the imagination, but she really was a pipe dream of Hitler and Raeder.

BTW, thanks again for the article. I had missed that the wreck of the ship had been found. I'd be really interested in seeing some pictures of her.