Description: The building of the U-boat bunker started in January 1941 and in September 1941 the first boat, U-372, used the first ready pen. The U-boat bunker at Brest was 333 metres wide, 192 metres long and roughly 17 metres high. The area covered was a record 52,000 square metres. The bunker was actually two structures, the first consisting of 13 pens, A to E and 1 to 8, the second of pens 9 and 10. The thickness of the roof was 3.6m in the first structure and 4.3 above pens 9 and 10. A second layer of concrete was poured over most of the roof making the best protection 6.2 metres.
It is still in use by the French Navy.