In the Orkneys, Prien, with masterly navigational skill, threads his way through the boom and net defences to enter U-boats Scapa Flow. Amazingly he remains undetected although surfaced until he reaches his first targets.

At 0100 hours Prien's first torpedoes strike the battieship HMS Royal Oak in the bows; inshore there is no reaction while U47 reloads and repositions. At 0123 three more torpedoes are fired and soon the battleship is riven by explosions which finally raise the alarm; 883 members of the crew are lost. Prien escapes to the open sea. This is a heavv blow to morale; according to Dônitz the sombre British radio announcement is his first intimation of the success of the raid.

The victonrious Prien arrives back at Wilhelmshaven to be welcomed by Raeder who promotes Dônitz to rear-admiral on the deck of U47. Prien and his crew fly to Berlin where he is decorated with the Knight's Cross of the Iron Cross by Hitler.
It is not all success for the U-boat fleet, however. During this month four of them are disabled in the English Channel, and from now on U­boats patrolling the North Atlantic are routed around the British Isles on passage to and from their home ports. The magnetic mme bas come into its own as a bidden destroyer of surface vessels; British and German ships and aircraft lay thousands of them around harbours and shipping lanes.