Increasing concern during the 1930s about the threat of air attack led to large numbers of units of the part-time Territorial Army (TA) being converted to anti-aircraft (AA) gun and searchlight roles in the Royal Artillery (RA) and Royal Engineers (RE), and higher formations became necessary to control them.

[4][5][6] The AA Divisions were unlike field formations: they were established to organise training and later exercise operational command in the static conditions of home defence, but relied entirely on the Home Forces commands for logistic support, supplies, and heavy repairs.

[5] The deterioration in international relations led to a partial mobilisation in June 1939, and a proportion of TA AA units manned their war stations under a rotation system known as 'Couverture'.

[48] The HAA guns were deployed in the defended areas as follows:[49] During the period of the Phoney War, the AA defences of NW England were not tested in action, and the time was spent in equipping and training the TA units.

AA Command also had to provide equipment and units to the British Expeditionary Force assembling in France.

[3][51][52][53] He was replaced by Maj-Gen Charles Cadell, recently returned from commanding the AA defences of Malaya.

[48][57] As the Battle of Britain fought over southern England in the summer of 1940 developed into the night bombing of the Blitz in the autumn, AA Command continued to expand.

[60] During the winter of 1940–41, the division was composed as follows:[58][61][62][63] The night raids continued into the following Spring, during which period Liverpool and its docks along the Mersey became the most heavily bombed area of Britain outside London, with particularly heavy attacks in December 1940 (the Christmas Blitz); in April 1941; and again the following month (the May Blitz).