Source: not available
In reality, during WWII no German aircraft carrier took part in any Naval action. The Nazis had plans to build a total of four carriers and almost finished one of them.
Her name was the KMS Graf Zeppelin and though launched in December 1938 she was never over 80% completed. Construction delays, lack of aircraft, and bitter disputes between Air Marshall Herman Goering and the Navy ensured that the ship was doomed to become scrap metal.
This film was released in 1944, so it would make sense the film makers would anticipate a German "Flattop".