On the Loire estuary in western France stands one of the largest structures the Second World War left behind: the former U-boat base of Saint-Nazaire. Built by Germany in 1941 and 1942, it sheltered submarines that attacked Allied convoys in the Atlantic. For the Allied air forces it became one of the most frustrating targets of the war.

Concrete Against the Atlantic

After the fall of France in 1940, Germany gained ports on the Bay of Biscay that put its U-boats hundreds of miles closer to the Atlantic convoy routes. At Lorient, Brest, La Pallice, Bordeaux and Saint-Nazaire, the Organisation Todt built enormous concrete shelters. At Saint-Nazaire more than 4,600 workers completed the bunker’s 14 pens, eight of them dry docks for repair, by 1942. A covered lock, to let U-boats reach the pens protected from the air, followed in 1943 and 1944. Sources differ on how much concrete was used, from about 313,000 to nearly 500,000 cubic metres, and on the roof, which the French government’s heritage site gives as 4 metres and the local tourist office as up to 9.6 metres in places as layers were added.

Flak City

The US Eighth Air Force began attacking the Biscay U-boat bases in the autumn of 1942. On 9 November 1942, 31 B-17s and 12 B-24s bombed Saint-Nazaire, losing three aircraft with 22 damaged. Raids continued through 1943. The port’s anti-aircraft defences were so dense that crews called it “Flak City”. In all, Saint-Nazaire was attacked about 50 times. General Carl Spaatz called the pens hard, maybe impossible, nuts to crack: the bombs of the day could not penetrate the roof, and the U-boats inside were untouched. The town around the base was not so lucky. Some 80 to 85 percent of Saint-Nazaire was destroyed and hundreds of civilians were killed; most residents had left by spring 1943.

The Man Who Fell Into the Station

One of the strangest stories of the air war happened over Saint-Nazaire. On 3 January 1943, Staff Sergeant Alan Magee, ball turret gunner on the 303rd Bomb Group B-17 “Snap! Crackle! Pop!”, was thrown from the stricken bomber without a parachute at more than 20,000 feet. He crashed through the glass roof of Saint-Nazaire’s railway station and survived, badly injured, to spend the rest of the war as a prisoner.

The Commandos and the Dry Dock

The U-boat bunker was not the only target. Beside it lay the huge Normandie dry dock, the only dock on the Atlantic coast big enough for the battleship Tirpitz. On 28 March 1942, in Operation Chariot, British commandos rammed the old destroyer HMS Campbeltown, packed with explosives, into the dock gate. Of the 612 sailors and commandos who took part, 169 were killed and 215 captured; five Victoria Crosses were awarded. Campbeltown exploded at midday, putting the dock out of action until 1948.

A Fortress to the End

After D-Day, the Germans held Saint-Nazaire as a fortress with a garrison of some 24,000 men. It was one of the last Atlantic ports to surrender, on 11 May 1945, three days after the end of the war in Europe. The bunker was too massive to demolish. Today it houses the Escal’Atlantic museum of ocean liners, the LiFE contemporary arts space and the VIP music venue, and visitors can walk across its roof for views over the port and the estuary.

What the Popular Description Gets Right

The usual description is accurate in outline: 14 pens, built in 1941 and 1942, a roof that the bombing never pierced while the town around it was flattened, the 1942 commando raid with a destroyer rammed into the dry dock, and the Escal’Atlantic museum and rooftop walk today. Figures for the concrete and roof thickness vary between sources, so the 480,000 cubic metres and nine metres often quoted are best taken as approximate.

Sources: French Ministry of the Armed Forces, Chemins de mémoire, “Submarine base, Saint-Nazaire”; Saint-Nazaire Tourisme; U-boat Bases research site, Saint-Nazaire; AvGeekery, “Saint-Nazaire: The U-Boat Base That Defied 2,000 Allied Sorties”; Historic Wings, “The Miracle of St. Nazaire” (2013); Commonwealth War Graves Commission (2022).