Norwegians started planning for a new attempt of stopping the heavy water production by ground operations, fearing civilian casualties by Allied bombing, but was overruled by British and American authorities. The Americans had wanted the sabotage to stop the whole plant, not just the high concentration plant. Since spring -42 they had wanted to bomb Vemork and from September Vemork was given priority as bomb target. The American "Eight Air Force" had been transferred to Britain in the summer of -42 for daylight bombing on the continent. High priority was given to halt German nuclear research by bombing, and bad news from Norway put Rjukan back at the top of the list. General Groves, commander of the American (nuclear) Manhattan-project, argued for a bombing raid to end the heavy water problem once and for all. Combined Chiefs of Staff, pressed by the Americans, at last agreed to bomb Rjukan. Eight Air Force was to carry out a precision daylight raid.
The Norwegian government in London was neither consulted nor informed, but in order to limit civilian casualties, the raid was precisely timed for the half hour just before noon on November 16 1943, when workers would have left the plant for lunch. The task was to bomb the electrolysis facilities used for production of "high explosive".
Nov. 16 at 1143 hours the first of 143 B-17 Flying Fortress from Eight Air Force started bombing. Coming in low (altitude of 3-4 000 m in 6 formations), dropping a total sum of 435 tons high explosive bombs, the power plant receiving 4 hits, damaging only two machines, two bombs hit the hydrogen plant smashing the roof. In the high conventration plant, one shrapnel damaged a cell, with the loss of 60 kg heavy water. Several houses, a school and a bomb shelter were hit, causing the lives of 22 civilians.
The Americans called this "pinpoint" bombing, but the fact of very few full hits and bombs almost 20 km from target illustrates the inaccuracy of high-altitude bombing. 15 minutes later 39 B-124 released over 70 tons of bombs over Rjukan, only 12 of the bombs actually damaging the nitrogen plant itself.
The damages were limited, nevertheless the bombing succeeded in shutting sown the plant. The Germans were convinced there was no point in trying to put the high concentration plant back into operation again. The heavy water equipment was dismantled and sent to Germany.
The bombing over Rjukan caused Norwegian protest and exchange of diplomatic notes, because the loss of civilian lives, planning of new sabotage operations and because the production of fertiliser were hit. The special dimensions of the heavy water production explains the Allied concern; they found it "extremely dangerous" if the Germans got hold of large quantum's of heavy water, because they could not assume that the Germans did not know as much in this field as the Allied.