 Britain 's Naval Intelligence Division first proposed a commando raid on the dock in late 1941 . When the German battleship Tirpitz was declared operational in January 1942 , the Royal Navy ( RN ) and Royal Air Force ( RAF ) were already drawing up plans to attack her . <unk> from Combined Operations Headquarters were looking at potential scenarios if Tirpitz escaped the naval blockade and reached the Atlantic . They decided the only port able to accommodate her was St Nazaire , especially if , like the Bismarck , she was damaged en route and needed repairs . They came to the conclusion that if the dock at St Nazaire were unavailable the Germans were unlikely to risk sending Tirpitz into the Atlantic . 
