not affected by the British commando raid in March 1942, whose main objective were the Normandie dock gates. Norway Norway is to some extent ruled by its weather. Building submarine pens was often hampered by snow and ice; the ground might have been chosen, but the occupation of France only a few months after Norway's surrender rather overshadowed the Scandinavian country as far as bunkers for U-boats was concerned. Nonetheless, a requirement for protection was identified. With the liberation of France in 1944, Norway regained its importance, but for barely a year. 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. However, with the project running six months late, plans for the second storey were abandoned. Bergen Control of the Bergen project came under the German Naval Dockyard. Construction of "Bruno" commenced in 1941, with a Munich-based firm taking the lead. A shortage of labour, along with the acquisition of raw materials in sufficient quantities and poor weather, was always going to cause problems. Specialised machinery had to be imported, as did accommodation that could stand up to the harsh Norwegian winter. In a bid to increase its protection, the bunker had granite blocks, each about a cubic metre in size, positioned on its roof. The shortage of cement ensured that the blocks could not be properly stuck down. Trondheim "Dora I" was started in 1941, shortly after Operation Barbarossa, the invasion of the Soviet Union. It was constructed by Soviet prisoners of war. Despite any number of precautions being taken when putting in the foundations, "Dora I" developed a noticeable sag of . It did not seem to bother the submariners as much as the builders. Work on "Dora II" started in 1942, but it was not completed by the end of the war. The Allied bombing offensive U-boat facilities first became a bombing priority in March 1941 and again during the Combined Bomber Offensive. The bunkers did not suffer as much as their surroundings until August 1944 when a new type of bomb was used against them, the "Tallboy" bomb. U-boat yards and pens were the primary objectives for the US Eighth Air Force from late 1942 to early 1943. In the course of the war, the Allies used various tactics and weaponry against German U-boat pens. For example, The