104 Royal Horse Artillery (Essex Yeomanry) (TA) was converted from 104 (Essex Yeomanry) Field Brigade RA (TA) in November 1938 with three batteries. It was reduced to two batteries in late 1938 and in September 1942 went back to three batteries. In January 1942, 414 Battery was detached and sent to Burma (Myanmar). 104 Royal Horse Artillery (Essex Yeomanry) (TA) was placed in suspended animation in March 1946 and reconstituted as 304 (Essex Yeomanry) Field 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.
| 3 Sep 39 |  |
Eastern Command | Chelmsford, Essex, UK |
| Nov 39 | 1 Cavalry Division | UK | |
| Jan 40 | 1 Cavalry Division | Palestine | |
| Sep 40 |  |
13 Corps | Baggush Box, Egypt |
| Mar 41 |  |
2 Support Group | N Africa |
| Apr 41 | Tobruk Garrison | Tobruk, Libya | |
| Dec 41 |  |
8 Army | N Africa |
| Mar 42 | 1 Armoured Brigade Group | N Africa | |
| Jun 42 | |
8 Army | N Africa |
| Jul 42 |  |
4 Armoured Brigade Group | N Africa |
| Jul 42 |  |
Middle East Forces | N Africa |
| Sep 42 |  |
8 Armoured Division | N Africa |
| Sep 42 |  |
10 Armoured Division | N Africa |
| Oct 42 | |
10 Armoured Division | Alamein, Egypt |
| Jan 43 | |
10 Armoured Division | Syria |
| Sep 43 | |
10 Armoured Division | N Africa |
| Jun 44 | |
Middle East Forces | N Africa |
| Sep 44 | |
8 Army | Italy |
Batteries
| 3 Sep 39 | 339, 414 |
| Jan 42 | 339 – 414 Battery detached to Burma |
| Apr 42 | 339, 519 |
| Sep 42 | 339, 463, 519 |
Equipment
| Sep 40 | 8 x 18 pdr Guns, 8 x 4.5 inch Howitzers |
| Apr 41 | 16 x 25 pdr |
| Sep 42 | Stuart Observation Post Tanks |