Structure of the British Army in 1939

In September 1939, the British Army was in process of expanding their anti-aircraft and mobile (including armoured) assets. Among these new changes was the formation of Anti-Aircraft Command which was formed on 1 April 1939, and the 1st Armoured Division formed in 1937.

Source: Wikipedia — Structure of the British Army in 1939 (CC BY-SA 4.0)