121 (Leicestershire Regiment) Light Anti-Aircraft Regiment RA (TA) was converted in January 1942 from 44 Searchlight Regiment. The Regiment served in Anti-Aircraft Command until May 1943 when it came under Home Forces. It went to Normandy with 8 Corps and stayed with them until the end of the war. Left behind on the breakout from Normandy, the Corps caught up again at Venray in Holland in September 1944. 121 (Leicestershire Regiment) Light Anti-Aircraft Regiment RA (TA) was placed in suspended animation in February 1946 and re-constituted as 579 (The Royal Leicestershire Regiment) Light Anti-Aircraft Regiment RA (TA) in January 1947.
Illustrations of the formation badges under which a unit served or supported are given. This is no guarantee that the unit used this formations badge.
| Feb 42 | Formed from 44 Searchlight Regiment | ||
| Feb 42 |  |
10 Anti-Aircraft Division, 62 Anti-Aircraft Brigade | Yorkshire, UK |
| Apr 42 | |
10 Anti-Aircraft Division, 39 Anti-Aircraft Brigade | UK |
| May 43 | Home Forces, 103 Anti-Aircraft Brigade | Norfolk, UK | |
| Mar 44 |  |
2 Army, 103 Anti-Aircraft Brigade | UK |
| Jun 44 |  |
8 Corps | Normandy, France |
| Sep 44 | |
8 Corps | Venray, Holland |
| Feb 45 | |
8 Corps | Venlo, Holland |
| Apr 45 | |
8 Corps | R Elbe, Germany |
Batteries
| Feb 42 | 396, 397, 398, 399 |
| Oct 42 | 396, 397, 399 |