I have just been able to visit the submarine pens at Lorient. Most of the pens are now used by industrial units and are not accessible.
The doc shown in the pictures is called Keroman one. Admiral Doneiz had his headquarters based close to the at Kernevel until the Dieppe raid by British forces in 1942. He then moved his HQ to Paris.
The concrete is over three meters thick in places. The roof has large air gaps which you can walk through. This is what made the pens so effective against allied bombing.
Allied bombing was ineffective and the town of Lorient was reduced to rubble. A 'tall boy bomb' was dropped on the roof of the 'dome' (i have no picures) and this just practically bounced off causing no damage.
The pictures do show some bomb damage to parts of the building. As you can see alot of the original fixings are still in place.
One of the pictures shows a part sunken ship in the harbour. This was done by the Germans to prevent torpedos being dropped by allied fighters.
The memorial is for Jaques Stosskopf (27 November 1898 – 1 September 1944) held the post of deputy director of naval construction at the Lorient arsenal. From September 1940, under the guise of collaboration with the Germans, he used his position to inform Allied forces of submarine movements at Lorient. He was denounced and arrested by the Gestapo in 1944. He was executed at Struthof camp in Alsace. He was posthumously awarded the Legion of Honour in 1945. The submarine base at Lorient was given his name in July 1946.
Unfortunatly I could not do the whole tour as I had a young family in tow!! I did get chance however to look in a French submarine that was used during the cold war. (I will upload the pics) The French after the war took over the base and used it themselves.
I hope the pictures give a good understanding of the size and scale of the building as they were so big. Hope this is of some interest. It is well worth a trip but they only do English speaking tours on certain days.