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.

It consisted of HQ and Nos 459–461 Companies (later Batteries) based at High Croft, Dyke Road, in Brighton (now Quebec Barracks of the Army Reserve).

537 S/L Battery joined the regiment on 11 March 1941[2] By early 1944, with the lower threat of attack by the weakened Luftwaffe, AA Command was forced to release manpower for the planned invasion of Normandy (Operation Overlord).

[2][16][17] As the threat from the Luftwaffe waned further after D Day, the War Office warned in June 1944 that AA Command would have to release manpower to provide reinforcements to 21st Army Group fighting in North West Europe.

[2][5][6][8][18] When the TA was reconstituted on 1 January 1947, 70th S/L Rgt reformed at Brighton as 605 (Mobile) Heavy Anti-Aircraft Regiment, RA (Sussex), forming part of 106 AA Bde.