20 Light Anti-Aircraft Regiment RA (TA) was formed at Cardiff, in December 1938. The Regiment served in the UK until June 1944 when it moved to France. It fought through North West Europe under 21 Army Group. It was placed in suspended animation in May 1946. 20 Light Anti-Aircraft Regiment RA (TA) re-constituted as 520 (Glamorgan) 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 |  |
Western Command | Cardiff, Glamorgan, UK |
| Mar 44 |  |
2 Army | UK |
| Jun 44 | |
2 Army | Normandy, France |
| Sep 44 |  |
GHQ Anti-Aircraft Troops, 105 Anti-Aircraft Brigade | Port-en-Bessin, France |
| Sep 44 | |
GHQ Anti-Aircraft Troops, 105 Anti-Aircraft Brigade | Caen, France |
| Dec 44 | |
GHQ Anti-Aircraft Troops, 105 Anti-Aircraft Brigade | South Scheldt, Belgium |
| Dec 44 | |
GHQ Anti-Aircraft Troops, 101 Anti-Aircraft Brigade | Brussels, Belgium |
| Apr 45 | |
GHQ Anti-Aircraft Troops, 101 Anti-Aircraft Brigade | Rhine Bridges |
Batteries
| Sep 39 | 62, 63, 64, 65, 66, 94 |
| Jul 40 | 62, 63, 64, 65, 94 |
| Jul 41 | 62, 63, 64, 65, 244 |
| Dec 41 | 62, 63, 65, 244 |
| May 42 | 62, 63, 244 |
| Jul 42 | 62, 63, 244, 371 |
| Jun 43 | 62, 63, 244 |
| Mar 44 | 62, 63 |