20 Anti-Aircraft Z Regiment RA formed in October 1942 at Inniscairn, Bath Road, Reading with three batteries. The Regiment disbanded in March 1945.
| Oct 42 | Formed | Reading, Berkshire, UK | |
| Oct 42 |  |
1 Anti-Aircraft Group, 38 Anti-Aircraft Brigade | London, UK |
| Apr 43 | |
3 Anti-Aircraft Group | UK |
| Apr 44 | |
Became 20 Anti-Aircraft Area Mixed Regiment | Swindon, Wiltshire, UK |
| Mar 45 | Disbanded |
Batteries
| Oct 42 | 111, 143, 198 |
| Dec 42 | 111, 143, 220 |
Batteries manned by Home Guard
| Battery | Home Guard Unit | Date from |
| 111 Battery | 101 Oxfordshire (Mixed) | Oct 42 |
| 143 Battery | 101 Gloucestershire (Mixed) | Nov 42 |
| 220 Battery | 101 Wiltshire (Mixed) | Oct 42 |