She was constructed as an experiment in Hamburg and her small size meant that she was completed in just four months, following which she conducted extensive trials in the Baltic Sea and off the Norwegian coast in an effort to gain an idea of the capabilities of the boat.

By the first few months of 1945, with the war drawing to a close, it was hoped new lessons could be learnt, and defeat potentially delayed by the insertion of some of these boats into the coastal waters of the United Kingdom.

The boats were unsuccessful, largely because of the professional nature of veteran Allied naval commanders in their construction of convoys and their preparation of escorts.

The North Sea proved largely barren, as most shipping was concentrated in the heavily defended English Channel, as so it was nearly a month after leaving Horten Naval Base in Norway that U-2321 scored her first and only victory, torpedoing the unescorted 1,406 GRT steamship Gasray.

Sailed to Loch Ryan in Scotland, U-2321 was allowed to rust and rot, the decaying hull destroyed as a naval gunfire target on 27 November 1945 along with all the other surrendered Norwegian U-boats.