120th Heavy Anti-Aircraft Regiment, Royal Artillery (120th HAA Rgt) was an air defence unit of the British Army during World War II.

All the enemy activity in April consisted of raids passing over South Wales on their way to attack targets elsewhere, with the guns being engaged on the nights of 3/4, 7/8 and 15/16 April, the latter night being a long engagement giving the gunners good practice in firing at 'unseen' targets under control of GL Mk.

The Welwyn Battery was a prewar Territorial Army unit that had seen heavy action during the Battle of France in 1940 and the Swansea Blitz in February 1941.

[14] Then in mid-January 1943, 120th HAA Rgt moved out of 26 AA Bde's area and came under direct War Office control to mobilise for overseas service as a defended ports unit on a three-battery establishment (248, 381, 384 Btys).

[3][12] After two months at the mobilisation centre at Easthampstead in Berkshire the regiment sailed from Liverpool on 14 March and disembarked at Port Tewfik in Egypt on 6 May.

[3] At the end of October 1943, the regiment was 'diluted' (as the process was officially described) by a draft of Basuto troops from the African Pioneer Corps to be trained as gunners, releasing a similar number of British Other Ranks for duties elsewhere.