Submarine pen
Among the first forms of protection for submarines were some open-sided shelters with partial wooden foundations that were constructed during World War I.
It was soon realized that such a massive project was beyond the Kriegsmarine, and the Todt Organisation (OT) was brought in to oversee the administration of labour.
The incessant air raids caused serious disruption to the project, hampering the supply of material, destroying machinery, and harassing the workers.
Machinery such as excavators, pile drivers, cranes, floodlighting, and concrete pumps (which were still a relatively new technology in the 1940s) was temperamental, and in the case of steam-driven equipment, very noisy.
[4] Bunkers had to be able to accommodate more than just U-boats; space had to be found for offices, medical facilities, communications, lavatories, generators, ventilators, anti-aircraft guns, accommodation for key personnel such as crewmen, workshops, water purification plants, electrical equipment, and radio testing facilities.
This story was gleaned from a similar situation in Le Havre in France when captured U-boat men were interrogated by the British.
Pens protecting construction of the Type XXI submarine were located in Hamburg (Blohm & Voss), Bremen (AG Weser), and Danzig (F.
Post-war, it was briefly used as a test site for British and American bombs (most of the damage done to the bunker was inflicted at this time[10]) before becoming a storage facility for the German Navy.
Off target bombs dropped in an air raid on the town caused a wave that crossed the Förde and enter the bunker.
The wash swamped U-4708 but U-170 alongside was saved because its captain, Oberleutenant zur See Hans-Gerold Hauber, had ordered all hatches on his boat to be closed, even though it was in the bunker.
[15] The German occupying forces built many U-boat pens in the Atlantic ports of France in Bordeaux, Brest, La Rochelle/La Pallice, Lorient, and St. Nazaire.
[16] These Atlantic bases expanded the u-boat striking range–allowing for voyages to the Mediterranean Sea, the west African coast, the Gulf of Mexico, and the United States' eastern seaboard.
By February 1942 the RAF had lost interest in the area; most of the town had already been destroyed and they did not possess large enough bombs to seriously threaten the bunker.
"Keroman I" was unique in that it required its U-boats to be "hauled out of the water, placed on a many-wheeled buggy and then transported into the bunker on a sliding bridge system."
[27] The pens were not affected by the British commando raid in March 1942, whose main objective were the Normandie dock gates.
With the liberation of France in 1944, Norway regained its importance, but for late in the war and past the prime of the U-boat's capabilities.
The Norwegian bunkers in Bergen and Trondheim were originally designed to have two floors, the lower one for U-boats, the upper one for accommodation, workshops and offices.
A shortage of labour, along with the acquisition of raw materials in sufficient quantities and poor weather, caused persistent problems.
However, a cement shortage led to these one cubic meter-sized blocks being placed insecurely, minimizing their protective effect.
Despite any number of precautions being taken when putting in the foundations, "Dora I" developed a noticeable sag of 15 cm (5.9 in), but it is believed to have little effect on submarine operations.
The Yugoslav People's Army used submarine pens as well, including ones on the islands of Vis and Brač or in Kotor Bay, carved inside natural hills.
The ones in Montenegro fulfilled their purpose, housing and protecting the submarines and missile boats from NATO aerial attacks during Operation Allied Force in 1999.
