The first of two volumes of the classified Air Historical Branch study of Fighter Command and the Air Defence of the United Kingdom. It covers pre-war expansion of the Command, the creation of the first integrated air defence system, and an account of Dunkirk and the Battle of Britain.

This volume deals with the development of Britain's air defences during the years leading up to the outbreak of World War II, and the development of the system during the early period of the war, leading up to the Battle of Britain. Originally classified as "secret," this report was written during the war as an internal Air Ministry history by Cecil James, a historian working for the Air Historical Branch.
The report describes the development of Fighter Command and the air defence network, often called the "Dowding System," and in doing so makes it clear how much of the groundwork for success was laid down in the 1920s by those working at a time when radar had yet to be developed. It was indeed the integration of technological advances such as radar and reasonably efficient radio telephones that allowed the defences to keep pace with the ever-increasing speed and sophistication of bomber aircraft. The result was the world's first truly integrated air defence network, designed to give its commanders botha picture of the enemy's air attacks as they developed and a sophisticated command system to assign and control the defending forces sent up to meet the enemy in the air.