The original plot, however, is similar to a real RAF mission. The novel's plot did not mention the nature of the target, only that it was a highly rated objective in Norway that could not be reached by the RAF until the Mosquito became operational. There was such a target, the molybdenum mine in Knaben, southern Norway. Typical of the mineral wealth that Hitler stated was worth the sacrifice of a significant portion of the "Kriegsmarine", Knaben could produce four-fifths of Germany's requirements for molybdenum, an important element in the production of armour plate. The mine at Knaben was too small to hit in a night raid, and sending heavy, long-range bombers in daylight would have met with disaster. Light bombers such as the Blenheim were ideal for the job, but did not have the necessary range. However, Knaben was within the range of the Mosquito, and 139 Squadron was given the task on 3 March 1943. Nine Mosquitoes were dispatched. All placed their bombs on target, though one failed to return. The target was out of action for some time and was later visited by the United States Army Air Forcess Eighth Air Force.