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 Regiment was placed in suspended animation in August 1944 and reconstituted as 500 Heavy Anti-Aircraft Regiment RA(TA) in January 1947.
| Apr 39 | Home Forces | Motherwell, Lanarkshire, UK |
| Sep 40 | 42 Anti-Aircraft Brigade, 12 Anti-Aircraft Division | UK |
| May 43 | Middle East Forces | N Africa |
| Jun 43 | 8 Army | N Africa |
| Sep 43 | 8 Army | 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 |
