When German forces took over France in mid-1940 the race began to protect their newly won territories with bunkers and batteries designed to repel any threats.
Alongside these were many sites designed to attack those threats, including V1 and V2 launch sites, each using massive amounts of concrete.
But all these sites are tiny in comparison to the massive constructions built to protect, service, and resupply the German Kriegsmarine’s U-Boat fleet – the most terrifying and effective weapons again the Allies at the time.
During the first year of the war over 1,000 Allied ships were sunk, more than half of these fell to the U-Boat menace which patrolled the Atlantic waters in search of targets.
Originally based in German ports such as Hamburg and Kiel, there was a need for U-Boats to be located closer to their main hunting grounds and so five sites were earmarked on the western French coast.
The five sites were based at exiting French ports at Brest, Lorient, Saint Nazaire, La Rochelle, and Bordeaux and they would become the largest structures built by the Nazis outside of Germany.
In July 1940 U-Boat U30 - built in Bremen and launched in August 1936 - had entered the harbour at Lorient, the first of many submarines which would operate from here over the next four years. At this point the U-Boats weren’t protected and so Fritz Todt, Hitler’s leading engineer, was tasked with building bunkers which would protect these vital assets.
Of the five sites, Lorient on the Keroman peninsula in Brittany was the first to be built and become operational. It would become the largest of them all with seven ‘cells’ built to protect up to 13 submarines at a time. The first three cells at Lorient were completed by June 30, 1941. Using a mixture of paid workers and slave labour, they took just three months to build.
Construction began at Saint Nazaire in February 1941 with the first three pens - No.s 6, 7, and 8 - completed by June 1941.
From June 1941 to January 1942, pens 9, 10, 11, 12, 13, and 14 were built. The site was finished with the completion of pens 1, 2, 3, 4, and 5 in June 1942.
Once completed, the Saint Nazaire U-Boat bunker measured 300m long and extended back into the town by 130m creating over 39,000 square metres of building. Standing 18m high, it's an imposing structure still today.
By 1942 work was progressing at the sites at La Pallice near La Rochelle and the inland U-Boat bunker in Bordeaux on the River Garronne. The plan was to be able to support up to 98 U-Boats with 30 at Lorient, 20 each at Brest and Lorient, 15 at Bordeaux, and 13 at La Pallice.
The sheer scale of the sites meant they were easily spotted by Allied aircraft and frequent bombing raids took place. However, few of the raids were effective at breaking through the 7m thick, steel-reinforced roofs. These roofs were also protected by ‘Fangrost’, a layer of reinforced concrete beams set in rows with spaces in between to create blast chambers which would dissipate the energy of bombs, including the famous ‘bunker-busting’ Tallboy.
It’s this sheer strength which ensures the bunkers are still visible today.

Saint Nazaire U-Boat base
Saint Nazaire is arguably the best preserved of all five sites in terms of its original fittings and this is possibly due to it not being an integral part of the French Navy’s plans and so was left to stand unused for many years. Today the site is in public use and so visiting is easy and you can access the large cells within the bunker.
Saint Nazaire was one of the most important ports for the Kriegsmarine and provided one of the largest dry docks for the repair of German ships. On March 28, 1942, aware that it could become the stopping point of Germany’s battleships, the British sent 600 commandos to attack Saint Nazaire as part of Operation Chariot.
The aim was to destroy the lock gates which would protect the battleships and allow them to be repaired, forcing them to return to other bases in Germany where they would have to run the gauntlet of the English Channel or North Sea.
Whilst the commandos fought the German garrison at Saint Nazaire, HMS Campbeltown – a US destroyer transferred to the Royal Navy – rammed the lock gates. Packed with explosives on a timer delay, the ship exploded the following day causing the lock gates to become inoperable. In fact, it wouldn’t be until 1948 when the dry dock was operational again.
Described as the ‘greatest raid of all’, five Victoria Crosses were awarded during Operation Chariot.
Following the Allied landings in Normandy and the push to liberate France, these sites became a place of last stands for German troops. Under orders, Lorient, Saint Nazare, and La Pallice were defended to the last man, and it was two days after the unconditional surrender of Germany on May 8, 1945, that Lorient and Saint Nazaire were finally liberated.