Our heaviest attack [of the week] took place on the night of the 20th-21st October when 138 medium and heavy bombers were despatched. A considerable weight of bombs were released within the various target areas, but results were difficult to assess except at Berlin, where a military objective and important marshalling yards were hit and at Grevenbroich and Cologne, where aluminium works were set on fire and several large fires were started in the vicinity of the Hohenzollern Bridge. At Bonn and Munster many explosions were caused when goods yards were bombed.
This night also marked the resumption of our attacks on Northern Italy after an interval of some six weeks. Targets in Turin, Milan, Aosta, Bergamo and Savona were attacked; at Aosta a large sheet of flame followed a direct hit on the steel works.
TNA CAB 66/13/5