On the night of 30–31 May 1942, RAF Bomber Command launched Operation Millennium against Cologne.

The raid was planned as a mass attack. Air Chief Marshal Arthur Harris wanted to send more than 1,000 aircraft over Germany in a single night. To reach that number, Bomber Command used front-line bombers, training aircraft and crews drawn together for the operation.

The target was Cologne, a major German city with industrial and transport value. Harris wanted to show that a large bomber force could damage German cities to a greater extent than smaller raids could.

Britain’s position in 1942 helps explain the importance given to the raid. The country had survived the Blitz, but the war in Europe was still being fought largely from the air and at sea. A return to the continent was not ready. Bomber Command gave Britain one of its few direct means of attacking Germany.

The raid needs care. Cologne was an industrial target, but it was also a city. The bombing caused heavy destruction, fires and civilian deaths. Homes, streets, churches, factories and public buildings were hit. The raid showed what a mass-bomber force could do and what it meant for people on the ground.

For Harris, Operation Millennium helped make the case for the bomber offensive. It showed ministers, the public and the RAF itself that Bomber Command could organise a raid on this scale. It also pointed towards the air war that followed, where German cities became regular targets and civilian damage became part of the campaign.

The Cologne raid is part of British military history, but it should not be treated solely as an operational achievement. It was a display of planning, numbers and air power. It was also an attack on a city. The date marks the scale of Britain’s bomber war and the civilian cost that came with it.