St Nazaire Raid - Background

Background

St Nazaire is on the north bank of the Loire 400 km (250 miles) from the nearest British port, it had a population of 50,000 in 1942. The St Nazaire port has an outer harbour known as the Avant Port, formed by two piers jutting out into the Atlantic Ocean. This leads to two lock gates before the Basin de St Nazaire. These gates control the water level in the basin so that it is not affected by the tide. Beyond the basin is the larger inner dock called the Basin de Penhoët, which can accommodate ships up to 10,000 tons. There is also an old entrance to the Basin de St Nazaire located northwest of the Normandie dry dock. Built to house the ocean liner SS Normandie, this dock was the largest dry dock in the world when it was completed in 1932. The "Old Mole" jetty juts into the Loire halfway between the southern pier of the Avant Port and the old entrance into the basin.

On 24 May 1941, the Battle of the Denmark Strait was fought between the German ships Bismarck and Prinz Eugen and the British ships HMS Prince of Wales and HMS Hood. Hood was sunk and the damaged Prince of Wales was forced to retire. Bismarck, also damaged, ordered her consort to proceed independently while she headed for the French port of St Nazaire, which was the only port on the Atlantic coast with a drydock able to accommodate a ship of her size. She was intercepted by the British and sunk en route.

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. Planners 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 was unavailable the Germans were unlikely to risk sending Tirpitz into the Atlantic.

Combined Operations examined a number of options while planning the destruction of the dock. At this stage of the war the British government still tried to avoid civilian casualties. This ruled out a bombing attack by the RAF, which at the time did not possess the accuracy needed to destroy the dock without serious loss of civilian life. The Special Operations Executive were approached to see if its agents could destroy the dock gates. They decided that the mission was beyond their capabilities because the weight of explosives required too many agents just to carry them. The RN were also unable to mount an operation, as St Nazaire is 8 km (5 miles) up the Loire estuary. Any naval ships large enough to cause sufficient damage would be detected well before they were within range.

The planners then examined whether a commando force could be used. There was an unusually high spring tide due in March 1942, which would allow a light ship to pass over the sand banks in the estuary and approach the docks, bypassing the dredged and presumably well-defended channel. It would still be too shallow for infantry landing ships, but specially lightened destroyers might succeed.