The thousand bomber raid was a joint US/UK bombing raid during World War 2 over the city of Cologne. The raid used the bomber stream tactic for the first time. The bomber steam was when the bombers would fly single column through the small gap between German radar defenses. This made it easier for Allied bombers to successfully complete their mission. Churchill expected a 10% loss (100 planes), the real loss was 4.% (41 planes)
The only place in Cologne that was not targeted was the Catherdral. THis was because the tower of the crathedral was used as an aid to nagivation for Allied pilots.