In 1941, the Butt Report revealed the extent of bombing inaccuracy: Churchill noted that "this is a very serious paper and seems to require urgent attention". The Area Bombing Directive of 14 February 1942 ordered Bomber Command to target German industrial areas and the "morale of...the industrial workers". The directive also reversed the order of the previous year instructing Bomber Command to conserve its forces – this resulted in a large campaign of area bombardment against the Ruhr area. Professor Frederick Lindemann's "de-housing" paper of March identified the expected effectiveness of attacks on residential and general industrial areas of cities. The aerial bombing of cities such as the Operation Millennium raid on Cologne continued throughout the rest of the war, culminating in the controversial bombing of Dresden in 1945.