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.

Lorient U-Boat base
The largest of the five sites, Lorient maintains a huge footprint on the Keroman peninsula with three main bunker sites – Keroman I, II, and III - plus dry docks, and two cathedral-like ‘Dombunkers’ for protecting and servicing U-Boats out of the water.
A fourth bunker, Keroman IVa was planned and building work was started – there’s a wall which can be seen connecting to KIII – but it was never finished. Keroman IVb never made it past the planning stage.

KI and KII are the largest of the buildings measuring 403m long and 143m wide, each with 3.5m thick roofs. KI was built between March and September 1941 and features five cells for five U-Boats while KII, finished in December 1941 could store seven submarines.
KIII – which was finished in July 1943 - was a more efficient build as although smaller at 168m by 142m it was able to protect 13 boats. The roof on this building is a much more substantial 7.5m thick.
The Dombunkers – for storing U-Boats out of the water – are both 81m long and 16m wide with 1.5m thick roofs. They were the first builds to be completed at the site in May 1941 and took advantage of existing port dry dock facilities used by French fishing boats.

Lorient now houses several museums which are easily accessible and tell the story of these impressive structures and their place in history. The view from the anti-aircraft positions on top of the building is incredible as is the view from the pontoons in front of the cells which gives you a sense of the scale of construction.
A few metres upstream on the River Scorff, opposite the Keroman bunkers is the Scorff bunker which was completed in August 1941 and consisted of two covered wet docks for protecting four U-Boats. This single structure measures 129m long by 51m wide.

Across the bay from the Lorient site at Larmor Plage, a HQ was established by Kriegsmarine commander Admiral Karl Donitz where he would oversee the movements of the U-Boats from this new base.
One of the most fascinating stories surrounding Lorient is the non-German visitors who stayed here. Remarkably, it wasn’t only Kriegsmarine submarines which visited Lorient as two Japanese subs also docked, both bringing war materials and returning with technology which would help their war effort including aircraft jet engines and state of the art torpedoes.

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.