173 Field Regiment RA was formed from 7 Defence Regiment RA in January 1942 with three batteries. It became a Home Defence unit guarding the Lincolnshire coast. At the end of 1942 the Regiment and Division were downgraded further to Reserve units. The Regiment was disbanded in March 1943 at Grimsthorpe Castle, its batteries transferred to 180 Field Regiment and reformed in July with four batteries at Park Villa, Alford. The new unit then became a Reserve Regiment providing replacements for units overseas. It continued in this role with both 76 and 47 Infantry Divisions which were designated Reserve Divisions until it was disbanded. 173 Field Regiment RA was disbanded in January 1945 less 138 Battery which went to 117 Field 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.
| Jan 42 | Formed from 7 Defence Regiment | Horncastle, Lincolnshire, UK | |
| Jan 42 |  |
48 Infantry Division | UK |
| Mar 43 | Batteries to 180 Field Regiment RHQ disbanded |
Bourne, Lincolnshire, UK | |
| Jul 43 | Re-formed | Alford, Lincolnshire, UK | |
| Nov 43 |  |
76 Infantry Division | UK |
| Sep 44 |  |
47 Infantry Division | UK |
| Jan 45 | Disbanded |
Batteries
| Jan 42 | A, B, C |
| Mar 42 | P, Q, R |
| Jan 43 | 156, 157, 158 |
| Jul 43 | 138, 156, 157, 158 |