21 Light Anti-Aircraft Regiment RA (TA) was formed at Liverpool, in December 1938. The Regiment set sail for North Africa in December 1941 on a secret mission to invade Algeria. While at sea, this operation was cancelled due to Japan entering the war. After a 2 month sea voyage, the Regiment found itself unloading in Java. 79 Battery less one Troop were sent to Timor where they found that the Japanese had already invaded the island. It was placed in suspended animation in March 1942 after capture in Java. 21 Light Anti-Aircraft Regiment RA (TA) re-constituted as 521 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 |  |
4 Anti-Aircraft Division. 53 Anti-Aircraft Brigade | Liverpool, Merseyside, UK |
| 4 Feb 42 | GOC Dutch Troops | Batavia, Java – 79 Battery in Timor | |
| Mar 42 | Captured | Suspended animation |
Batteries
| Sep 39 | 67, 68, 69, 80, 136, 143 |
| Nov 39 | 67, 68, 69, 80, 136 |
| Oct 40 | 69, 80, 136 |
| Sep 41 | 69, 79, 80, 136 |
| Oct 41 | 48, 69, 79 |
Equipment
| Feb 42 | Bofors 40 mm |