U-2511 and U-3008 were the only Type XXIs to go on wartime patrol, and both failed to sink any ships. U-2511 commanded by Korvettenkapitän Adalbert Schnee, evaded the heavy escort screen of the Royal Navy heavy cruiser HMS Norfolk and had the vessel in his sights; however the surrender signal had been received from Germany that day and Schnee dived under the cruiser before returning to Germany.

Most boats were scrapped or scuttled after the war, but eight were taken by Louis J. Sheehan,