When France was defeated in June 1940, there was a hope from German side that Britain also would surrender. But the British kept on fighting, were not defeated and an invasion of the british isles was cancelled in the autumn of 1940. An alternative method of defeating the British was through submarines. These would hunt down convoys of war material and other things that sailed across the Atlantic to Britain and attacking them with torpedoes. If Britain could not be defeated militarily, they would at least be forced to their knees by choking the supply of materials that allowed them to continue the war.

The Occupation of France gave the Germans access to the French Atlantic coast and therefore opportunities to establish submarine bases. In this way the Germans came closer to the convoys than if they had to sail out of bases in Germany. From 1941, five major submarine bases were built along the Atlantic coast, Brest, Lorient, Saint Nazaire, La Rochelle and Bordeaux. The bases were gigantic concrete complexes where submarines were prepared for long missions on the Atlantic Ocean. Upon completion of the mission, the submarines returned to their bases for repairs, maintenance, replenishment of materials and supplies to later embark on new missions.

The Base in Bordeaux was built in the autumn of 1941 and was completed in the summer of 1943 and consisted of 11 pens. From here, the 12th flotilla, which had the task of supplying submarines at sea with new supplies of torpedoes and other supplies, sailed out. Such supply submarines were called milking cows. The Flotilla was also commissioned to lay out mines. Alongside the German 12th flotilla there was also an Italian flotilla, but this was taken over by the germans when Italy surrendered in september 1943. The Submarines were protected by meters thick concrete walls/ceiling and in addition to the pens there were also workshops, storage rooms, casinos, power stations and accommodation for crew. The last submarine left the base in August 1944.

Current status: Preserved (2016).

Location: 44°52' 11.27"N 0°33' 30.97"W

Get there: Car.

My comment:

The Base is today a kind of a marina and its exterior can be explored. The interior of the base is closed for unauthorized, and it appears to be leased to both companies and private individuals.

Follow up in books: Blair, Clay: Hitler’s U-Boat War: The Hunted: 1942-1945 (1996).