"The gun battery was named Karola and was built between 1942 and 1944 by the German navy. On 12 September 1944, the Allies had surrounded the entire fort and a long siege began. The base was defended by 20,000 German soldiers and the siege continued until the capitulation. During this time, all supplies to the base was provided by u-boats.
The third May 1945 the last u-boat (U-255) arrived with fuel and supplies to the besieged base. It left the base again two days later and the eighth May the German garrison surrendered to the Allies."