The St Nazaire Raid or Operation Chariot was a British amphibious attack on the heavily defended Normandie dry dock at St Nazaire in German-occupied France during the Second World War. The operation was undertaken by the Royal Navy (RN) and British Commandos under the auspices of Combined Operations Headquarters on 28 March 1942. St Nazaire was targeted because the loss of its dry dock would force any large German warship in need of repairs, such as Tirpitz, sister ship of Bismarck, to return to home waters by running the gauntlet of the Home Fleet of the Royal Navy and other British forces, via the English Channel or the North Sea.

The obsolete destroyer HMS Campbeltown, accompanied by 18 smaller craft, crossed the English Channel to the Atlantic coast of France and was rammed into the Normandie dock gates. The ship had been packed with delayed-action explosives, well hidden within a steel and concrete case, that detonated later that day, putting the dock out of service until 1948.

A force of commandos landed to destroy machinery and other structures. German gunfire sank, set ablaze, or immobilized virtually all the small craft intended to transport the commandos back to England. The commandos fought their way through the town to escape overland but many surrendered when they ran out of ammunition or were surrounded by the Wehrmacht defending Saint-Nazaire.

Of the 612 men who undertook the raid, 228 returned to Britain, 169 were killed and 215 became prisoners of war. German casualties included over 360 dead, some of whom were killed after the raid when Campbeltown exploded. To recognise their bravery, 89 members of the raiding party were awarded decorations, including five Victoria Crosses. After the war, St Nazaire was one of 38 battle honours awarded to the commandos. The operation has been called "the greatest raid of all" in British military circles.

Combined Operations Headquarters was a department of the British War Office set up during Second World War to harass the Germans on the European continent by means of raids carried out by use of combined naval and army forces.