On 1 September 1939, Germany invaded Poland. It was the start of a conflict that would erupt over every continent, see the deaths of tens of millions of people, much of central Europe destroyed, the development of jets, ballistic missiles and computers as well as the atomic bomb.

1944 saw the invasion of France on D-Day, 6 June, supported by a massive airborne assault and heavy close air support. In the Battle of the Philippine Sea, the US Navy scored a decisive victory against Japan, inflicting heavy losses on Japanese naval aviation. Meanwhile, the bombing of German cities continued, the Italian monastery of Monte Cassino was destroyed from the air and Tokyo was bombed for the first time since the Doolittle Raid of 1942. London and other British cities were in the front line once again as attacks using V1 flying bombs and, later, V2 rockets began and the Me 262 jet fighter scored its first victory.