3 (Ulster) Searchlight Regiment RA (SR) was formed in September 1939 in Northern Ireland, with four batteries. The Regiment went to France in December 1939. On return it served in South West England until conversion. 3 (Ulster) Searchlight Regiment RA (SR) was converted to 4 (Ulster) Light Anti-Aircraft Regiment in January 1942.
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.
| Sep 39 | 3 Anti-Aircraft Division, 3 Anti-Aircraft Brigade | Belfast, UK | |
| Nov 39 | Home Forces | Borden, Hampshire, UK | |
| Dec 39 | 2 Anti-Aircraft Brigade | France | |
| Mar 40 | 5 Anti-Aircraft (Searchlight) Brigade | France | |
| May 40 | Granted title (Ulster) | ||
| Jun 40 |  |
8 Anti-Aircraft Division, 64 Anti-Aircraft Brigade | South West airfields, UK |
| Jan 42 | Became 4 Light Anti-Aircraft Regiment |
Batteries
| Sep 39 | 9, 10, 11, 12 |
Equipment
| 1939 | Guy FBX 6×4 Searchlight Lorry |