121 (West Riding) Field Regiment RA (TA) was formed with two batteries at Bramley, Leeds in April 1939 as a duplicate of 69 Field Regiment. In February 1941 a third battery was formed in County Durham. In January 1944 121 (West Riding) Field Regiment RA (TA) was converted to 121 (West Riding) Medium Regiment RA (TA).
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.
(Title authorised February 1942)
| Apr 39 |  |
46 Infantry Division | Leeds, Yorkshire, UK |
| Apr 40 | |
46 Infantry Division | France |
| Jun 40 | |
46 Infantry Division | UK |
| Jul 40 | Home Forces | UK | |
| Oct 41 |  |
10 Army | Iraq |
| Dec 41 |  |
10 Indian Division | Iraq |
| Jun 42 | |
10 Indian Division | N Africa |
| Jul 42 |  |
British Troops Egypt | N Africa |
| Sep 42 |  |
23 Armoured Brigade | N Africa |
| Oct 42 | |
23 Armoured Brigade | Alamein, Egypt |
| Dec 42 |  |
8 Army | N Africa |
| Jul 43 | |
Middle East Forces | N Africa |
| Sep 43 | |
8 Army | Salerno, Italy |
| Jan 44 | Became 121 Medium Regiment |
Batteries
| Apr 39 | 275 (3rd West Riding), 276 (11th West Riding) |
| Feb 41 | 275, 276, 486 |
| Jun 42 | 275, 276 |
| Jun 43 | 161, 275, 276 – 161 Battery disbanded |
| Jan 44 | 275, 276 – converted to Medium Batteries |
Equipment
| Sep 42 | Valentine Observation Post Tanks |
| Oct 42 | 16 x 25 pdr Self Propelled Bishop |
