Introduction
The first anti-aircraft unit in the British Army was formed in 1920. The number of units grew steadily throughout the 1930’s, mainly by the addition of Territorial Army units. The decision was taken in 1936 that the air defence of the United Kingdom would be undertaken by the Territorial Army. This led to the formation of the first two anti-aircraft divisions in the U.K.

Anti-Aircraft Command was formed on the 1 April 1939, under the command of General Sir Alan BROOKE. He was not in post long, handing over to General Frederick Alfred PILE, who was to remain in command throughout the Second World War.

Formations
There were two anti-aircraft brigades within the Regular Army, both stationed at Aldershot and under Aldershot Command. The main bulk of anti-aircraft artillery within the British Army was provided by the Territorial Army. With the expansion of anti-aircraft artillery required to meet the increasing threat from Germany, several Territorial Army infantry battalions were converted into anti-aircraft units.

In December 1939, the 46 (North Midland) Division and the 47 (London) Division were both disbanded as infantry formations, and their headquarters staff used to form two new anti-aircraft divisions. The 47 (London) Division formed the 1 Anti-Aircraft Division; with the 46 (North Midland) Division forming the 2 Anti-Aircraft Division.

This remained the situation until 3, 4 and 5 Anti-Aircraft Divisions were formed in September 1938.