171 Field Regiment RA was formed from 2 Defence Regiment RA in January 1942 with three batteries. In February 1942 in joined 45 Infantry Division which had just been downgraded to a Home Defence Division. The Division covered the defence of the Essex coast. 45 Division with 171 Field Regiment spent most of 1943 training in Northern Ireland. The main purpose of the Division was now to provide trained replacements to units overseas. It converted in February 1945 to 171 Heavy Regiment and back to 171 Field Regiment RA in May 1945 at Bexhill on Sea Camp. The Regiment was now a Reserve unit, supplying replacements for other units, mostly in North West Europe. It disbanded in January 1946.
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.
| Jan 42 | Formed from 2 Defence Regiment | ||
| Feb 42 |  |
45 Infantry Division | UK |
| Feb 43 | |
45 Infantry Division | N Ireland, UK |
| Dec 43 | |
45 Infantry Division | UK |
| Aug 44 | Home Forces | UK | |
| Feb 45 | Became 171 Heavy Regiment | ||
| May 45 | Became 171 Field Regiment | Bexhill, Sussex, UK | |
| May 45 |  |
47 Reserve Infantry Division | UK |
Batteries
| Jan 42 | A, B, C |
| Mar 42 | P, Q, R |
| Jan 43 | 150, 151, 152 |
| May 45 | 7, 35, 36, 150, 151 |