The Combined Ops raid on St. Nazaire was codenamed Operation Chariot. H.M.S.
Campbeltown, ex-U.S.S.
Buchanan, was disguised as a German
torpedoboot and rammed into the lock gate of St. Nazaire in March 1942, denying the use of the largest dry-dock on the west coast of France to the Axis when the explosive charge in her bows blew up the lock gate - and some numbers of German sight-seers - the following day. The result was no more Atlantic or Channel-coast repair facilities for the big German battleships, which were now confined to northern waters.
Tirpitz was now a lot less dangerous without a secure Atlantic port in which to refit.
Well done, the Royal Marines and the British Army personnel who fought their way into the dock area installations and blew them into such a tangle that repairs were still incomplete by war's end. And the Royal Navy who got them there, even if it couldn't get them home again: most of the Marines and soldiers were killed or captured when it proved impossible to get away on the designated RN light vessels that were shot to pieces by an alert defence. Five Victoria Crosses were awarded for the action.
For further information, the best single-volume history of Operation Chariot is
Storming St. Nazaire by James Dorrian; 1998, Leo Cooper, Pen & Sword Books, London, ISBN 0 85052 419 9. It describes how the attack was compromised by a bombing raid by the R.A.F. that succeeded mainly in alerting the German garrison rather than distracting it - not 'Bomber' Harris' finest hour, for sure.