British U-class submarine

The British U-class submarines (officially "War Emergency 1940 and 1941 programmes, short hull") were a class of 49 small submarines built just before and during the Second World War. The class is sometimes known as the Undine class, after the first submarine built. A further development was the British V-class submarine of 1942.

At the start of the Second World War the U class was, with the British S and T-class submarines, the Dutch O 21 class and German Type VII one of the most advanced submarine classes in service.