Dönitz was encouraged in operations against warships by the sinking of aircraft carrier "Courageous". On 28 September 1939 he said, "it is not true Britain possesses the means to eliminate the U-boat menace." The first specific operation, named "Special Operation P", authorised by Dönitz was Günther Prien's attack on Scapa Flow which sank the battleship "Royal Oak". The attack became a propaganda success though Prien purportedly was unenthusiastic about being used that way. Stephen Roskill wrote, "It is now known that this operation was planned with great care by Admiral Dönitz, who was correctly informed of the weak state of the defences of the eastern entrances. Full credit must also be given to Lieutenant Prien for the nerve and determination with which he put Dönitz's plan into execution."