100 Anti-Aircraft Regiment RA (TA) was formed at Motherwell in April 1939. It was re-designated as 100 Heavy Anti-Aircraft Regiment RA (TA) in June 1940. The unit served in Anti-Aircraft Command until October 1942. It moved to North Africa in May 1943 and in August it went to Italy with the 8th Army. The Regiment was placed in suspended animation in August 1944. 100 Heavy Anti-Aircraft Regiment RA (TA) was reconstituted as 500 Heavy 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.
| Apr 39 |  |
3 Anti-Aircraft Division, 42 Anti-Aircraft Brigade | Motherwell, Lanarkshire, UK |
| Nov 40 |  |
12 Anti-Aircraft Division, 42 Anti-Aircraft Brigade | Scotland |
| May 42 | |
12 Anti-Aircraft Division, 57 Anti-Aircraft Brigade | Scotland |
| Jun 42 | |
3 Anti-Aircraft Division, 51 Anti-Aircraft Brigade | |
| Aug 42 | |
12 Anti-Aircraft Division, 51 Anti-Aircraft Brigade | Scotland |
| Oct 42 | Unbrigaded | UK | |
| May 43 |  |
Middle East Forces | N Africa |
| Jun 43 |  |
8 Army, 2 Anti-Aircraft Brigade | N Africa |
| Aug 43 | |
8 Army, 12 Anti-Aircraft Brigade | Italy |
| Aug 44 | Suspended animation |
Batteries
| Apr 39 | 304, 305 |
| Sep 40 | 304, 305, 321 |
| Apr 41 | 304, 305, 321, 406 |
| Jul 42 | 304, 305, 321 |