As the international situation deteriorated in the late 1930s, the threat of air raids on the UK led to the rapid expansion in numbers of anti-aircraft (AA) units manned by members of the part-time TA.

[1] It consisted of HQ and Nos 465–467 Companies (later Batteries) based at a newly built drill hall at Vicarage Road, Heston.

[2][15] The regiment supplied a cadre of experienced officers and men to 237th S/L Training Rgt at Holywood, County Down, where it provided the basis for a new 560 S/L Bty formed on 13 February 1941.

[2] However, as the threat of attack by the weakened Luftwaffe waned, AA Command was being forced to release manpower for the planned invasion of Normandy (Operation Overlord).

[2][22] Then the War Office warned in June that AA Command would have to release manpower to provide reinforcements to 21st Army Group fighting in North West Europe.