La Pallice, Sk U-Schleuse, K.V.Gr Süd La Rochelle,AOK 1 / KVA D, Charente Maritime

The original French built lock gate entrance to the port and you can just see the start of digging out the Schleuse.

83to103 - Abri ou soute (demolis).
104 - Tobruk avec tourelle de char.
123to125 - Cuve pr canon de 20 D.C.A. (AA).
129to133 - Cuve pr canon de88 D.C.A. (AA).
144 - Plateforme pr Mitrailleuse.
147 - Projecteur.
149 - Base Sous marine
150 - Couvert.

An Allied air photo of the French built lock gate entrance to the port with the protected German built Sk U-Schleuse next to it.
SK - Sonderkonstruktionen special construction type.
Schleuse - Sluice as in sluice gate, like a canal lock, allowing a boat/ship to enter the sluice at low tide, the water is then pumped into the sluice and when it is equal lo the inner harbour, the gate can open and allow the boat/ship into the port.
The SK Schleuse does exactly the same thing, but is covered in a concrete box, allowing the U-boat access at all times and protection if there is a bombing raid going on.
I believed that none of the Atlantic coast Schleuse's were ever used but I was totally wrong, this one was used right up until the end of the war to allow many U-Bootes to enter and remove important people and equipment to return to Germany as the war was ending..

Original external lighting, this would be used at night, but when the air-raid siren sounded. All lights would be extinguished.

72 unescorted aircraft of the USAAF Bomber Command attacked 16 September 1943 with a heavy concentration on the Sluice.