From beginning to end, World War II was an air war. Germany opened the conflict with drives across Poland, Belgium, Luxembourg, the Netherlands, and France during 1939 and 1940. Despite the fact that the bulk of the ground troops of the German blitzkrieg relied on horses for transport, the airborne component was modern. Dive-bombing Stukas became a familiar sight in European skies. The might of the Luftwaffe was never seriously challenged over mainland Europe in that first year of war. The French Air Force, although finally equipped with modern aircraft in reasonable numbers, crumbled through lack of communications and strategy.

Britain's Spitfires and Hurricanes, hurriedly flown to France to shore up its failing defences, were equally hurriedly flown home when it became apparent that the vital aircraft might be captured by the sheer speed of the German advance. Attempts to achieve air superiority over Britain in preparation for an invasion began with German attacks on shipping in the English Channel in July 1940, followed by aerial raids on British coastal installations and RAF bases, and day-and-night bombing attacks on London and other British towns and cities.

The fighter pilots of Britain's RAF won the Battle of Britain in 1940 by a narrow margin. The quality of their solidly built Hawker Hurricane and speedy Supermarine Spitfire interceptors was one vital factor. Equally important, the RAF was operating in the skies close to its own airfields, while the Luftwaffe had to return to bases all over northern France. The fact that the Spitfires and Hurricanes could return home, refuel, and be back in the air within half an hour tipped the otherwise unfavourable numerical balance back in Britain's favour. The vulnerability of German bombers such as the Heinkel He 111, Junkers Ju 88, and Dornier Do 17, with their liquid-cooled engines, relatively slow speed, and lack of defensive armament, also played a part.
Just as important, however, was the network linking radar stations to command centres that plotted the position of German aircraft and guided British fighter pilots towards their targets by radio. Electronic weaponry had emerged as a major factor in air warfare.

The high losses resulting from early attempts to bomb targets in Germany convinced the leaders of RAF Bomber Command to discontinue daylight precision attacks on specific targets in favour of night attacks.