At the time Norway was invaded in 1940, during World War II, the Knaben mines were one of the only molybdenum mines in Europe still in operation. The occupying German forces stationed about 1,000 men in the area, and established gun sites for anti-aircraft guns. The mine operations were the target for allied bombing twice in 1943. The first attack took place on 3 March, with 10 British de Havilland Mosquito strike fighters of No. 139 Squadron RAF participating. The second attack was on 16 November, when 130 American B-17 bombers from the Eighth Air Force (in its mission number 131) attacked the Knaben molybdenum mines in a raid against Norway.