21 Anti-Tank Regiment RA was formed in November 1938 by conversion of 21 Field Brigade RA with four batteries. In November 1946, RHQ and three batteries became 4 RHA. The identity of 21 Anti-Tank Regiment RA passed to 21 Field Regiment. In June 1947, RHQ 21 Field Regiment re-organised as RHQ 4 RHA and the identity of 4 RHA passed to RHQ 10 Anti-Tank Regiment.
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||1 Infantry Division||Aldershot, Hampshire, UK|
|Sep 39||1 Infantry Division||France|
|Jun 40||1 Infantry Division||UK|
|Nov 40||Cadre to form 74 Anti-Tank Regiment|
|Oct 41||Guards Support Group||UK|
|Jun 42||Guards Armoured Division||UK|
|Jun 44||Guards Armoured Division||NW Europe|
|Jun 45||7 Armoured Division||NW Europe|
|3 Sep 39||Q, Y, Z, BB|
|Sep 41||BB Battery to form 81 Anti-Tank Regiment|
|Jul 45||Q (Sanna’s Post), Y, Z, 2 (Minden)|