HMS Unshaken (P54) was a Royal Navy U-class submarine built by Vickers-Armstrong at Barrow-in-Furness. She has been the only vessel of the Royal Navy to bear the name Unshaken.

The British U-class submarines 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.