U-47 in Scapa Flow: the sinking of HMS Royal Oak 1939

At the outset of World War II, Scapa Flow was supposed to be the safe home base of the British Navy - nothing could penetrate the defences of this bastion. So how, in the dead of night, was Gunther Prien's U-47 able to slip through the line of protective warships to sink the mighty Royal Oak? This book provides the answer with an account of one of the most daring naval raids in history.