La Rochelle U-Boat Submarine Pen part 6

The construction of La Rochelle U-boat base started in april 1941. Work lasts day and night.
To make the building invulnerable to the bombardments, the Germans cover it with a flagstone of concrete and of steel an average thickness of 3.5 metres.
In November 1941, the first section of work is finished.
The bunker makes it possible to place 4 U-boats in 2 wet docks, and 5 others in the 5 accessible docks
With the increase in the number of the submarines in operations, the German staff decides to increase the number of places inside the U-bunker. A second section of work is undertaken in April 1942, in order to add to it 3 new pens.
The base finally consists of 10 cells making it possible to maintain 13 submarines 10 workshops and stores.
Cells 3 to 9 can be closed by tight hoppers, and be drained by powerful pumps.
To supplement the device, a new lock is built in July 1942, entirely protected by a bunker and only reserved for the passage of the submarines. The defense of the base is ensured by a whole anti-aircraft and anti-submarine device. Tethered balloons prevent bombardments at low altitude, whereas the positions of Flak (gun AA) and the Luftwaffe based in Laleu avoid the bombardments at higher altitude.
Other facilities on the base are electric power stations, torpedo bunkers etc