40 Light Anti-Aircraft Regiment RA (TA) was formed at Inverness in September 1939. After some time in Air Defence Great Britain, they became the divisional anti-aircraft unit in 51 Highland Division. They remained with 51 Division through North Africa and Sicily before returning to the UK. They moved with the Division to Normandy in June 1944. The Regiment was placed in suspended animation in March 1946. 40 Light Anti-Aircraft Regiment RA (TA) was re-constituted as 540 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.
| Sep 39 | Formed | Inverness, Inverness-shire, UK | |
| Feb 41 |  |
3 Anti-Aircraft Division, 51 Anti-Aircraft Brigade | North East Scotland |
| May 42 |  |
51 Infantry Division | UK |
| Aug 42 | |
51 Infantry Division | Egypt |
| Jul 43 | |
51 Infantry Division | Sicily |
| Nov 43 | |
51 Infantry Division | UK |
| Jun 44 | |
51 Infantry Division | Normandy, France |
| Sep 44 | |
51 Infantry Division | Le Havre, France |
| Sep 44 | |
51 Infantry Division | Sint-Oedenrode, Holland |
| Feb 45 | |
51 Infantry Division | Reichswald, Germany |
| Apr 45 | |
51 Infantry Division | Delmenhorst, Germany |
Batteries
| Sep 39 | 105, 140 |
| Nov 39 | 105, 140, 177 |
| Sep 41 | 105, 140, 268 |
Equipment
| Aug 42 | 48 x 40 mm Bofors Guns |
| Jun 44 | 40 mm Bofors Guns, 20 mm Polstens |
| Apr 45 | 40 mm Bofors Guns, 20 mm Polstens, 2 x M 51 Quad Brownings per Troop |