100 Light Anti-Aircraft Regiment RA was converted in December 1941 from 18th Battalion The Royal Fusiliers (City of London Regiment). The Regiment moved to Iraq in November 1942 and then to Egypt and Tunisia driving over 3,000 miles in a month. It went to Italy in September 1943 landing at Salerno and later fought at Anzio. 100 Light Anti-Aircraft Regiment RA was disbanded in January 1945.
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.
| Dec 41 | Formed from 18th Battalion Royal Fusiliers |
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| Dec 41 | Home Forces | UK | |
| Feb 42 |  |
56 Infantry Division | East Anglia, UK |
| Nov 42 | |
56 Infantry Division | Kirkuk, Iraq |
| Mar 43 | |
56 Infantry Division | Egypt |
| Mar 43 | |
56 Infantry Division | Tunisia |
| Sep 43 | |
56 Infantry Division | Salerno, Italy |
| Sep 43 | |
56 Infantry Division | Capua, Italy |
| Dec 43 | |
56 Infantry Division | Monte Camino, Italy |
| Feb 44 | |
56 Infantry Division | Anzio, Italy |
| Apr 44 | |
56 Infantry Division | Port Said, Egypt |
| Jul 44 | |
56 Infantry Division | Gothic Line, Italy |
| Nov 44 |  |
Allied Forces HQ | Italy |
| Jan 45 | Disbanded |
Batteries
| Dec 41 | 330, 331, 332 |