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.
Constructions at Brest and Saint Nazaire followed and 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.

Brest U-Boat bunker
Of all five sites, Brest is one of the most difficult to access as it stands as part of an active French Navy base to this day. It is surrounded by industrial buildings and although there are areas where the original concrete building it can be viewed from, access inside is forbidden.
The Brest U-Boat bunker was constructed from January 1941 to July 1942 and is a huge 333m by 192m with a 6.2m roof thickness. It was built to protect 20 boats in 10 dry docks and five wet docks.
Brest was attacked on over 80 occasions and suffered the most damage from Allied air raids in August 1944 when five Royal Air Force dropped Tallboy bombs penetrated the roof, although they were unable to cause damage to the insides of the bunker.
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, these sites were defended to the last man, and Brest was the first to be attacked by US forces – on July 27, 1944 – and while the last U-Boat left the bunker on September 4, it took until September 21 for the heavily defended site to be captured.
Other bases were able to hold out for longer and it was two days after the unconditional surrender of Germany on May 8, 1945, that Lorient and Saint Nazaire were finally liberated.
Brest was the location of the 9th Flotilla of which U-Boat U-96 was part of. This particular boat was the one which war correspondent and photographer Lothar-Gunther Buchheim spent time on in late 1941 where he chronicled the lives of the crew and created the now legendary book Das Boot.