High Quality Content by WIKIPEDIA articles! HMS Graph (pennant number P715) was a Type VIIC U-boat. Originally the U-570 of the German Kriegsmarine, she was captured and commissioned into the Royal Navy during World War II. She was the only German U-boat to be taken into Allied service and to see active service with both sides during the war. U-570 was laid down by Blohm & Voss at Hamburg in May 1940 and commissioned on 15 May 1941. After a series of short testing and commissioning trips in the Baltic, she moved to Norway where she carried out short training voyages and fired practice torpedoes.