Air Marshal Harris, commander since February, was responsible for the revitalization. He also was responsible for what came to be called the '1,000-plane' raids. By drawing in every operational aircraft and crew, including some in training units, Bomber Command was able to send 1,046 aircraft to Cologne on the night of 30 May 1942. They dropped 1,455 tons, and left the city burning fiercely, with more than 45,000 civilians homeless and 250 factories destroyed.
The second 1,000-plane mission sent 956 bombers against Essen. They did little damage to the city, and none at all to the Krupp works, the primary target. The third such mission was mounted against Bremen; 904 bombers dropped on its industrial heart, severely damaging one of the Focke-Wulf factories. Those three missions were the only giant raids for a while, as Bomber Command's strength would permit no more on that scale. A large force still could be mustered, as on the night of 30 July, when the RAF sent 630 bombers against targets in Dusseldorf.
So it was that before the USAAF had dropped a single bomb on a European target, the Royal Air Force was consistently sending a force of several hundred bombers against major industrial cities. Harris was demonstrating his concept of strategic bombing. It had to be done at night, by large numbers of bombers, with cities as targets, and with the simplistic goal of burning the Germans out of their homes and, not incidentally, killing as many people as possible.
It was a doctrine on a collision course with American plans for the employment of their bombers.