Five of the six submarine minelayers were lost during the war, and the history of the Class produces an unhappy diary of events:
5th May, 1940: Seal, the last of the class to be constructed, was captured as a wreck in the Kattegat and recommissioned as a German U-Boat. She was finally scrapped in 1941.
24th June, 1940: Grampus was lost on active service in the Mediterranean - cause unknown.
1st August, 1940: Narwhal was lost on active service off Norway - cause unknown.
October 1941: Cachalot was lost on active service - details unknown.
19th January, 1945 (approximately): the first-of-class Porpoise was lost on active service in the Malacca Strait - probably sunk by aircraft.
