78 (Duke of Lancaster’s Own Yeomanry) Medium Regiment RA (TA) was formed as a duplicate of 77 (Duke of Lancaster’s Own Yeomanry) Medium Regiment RA (TA) in April 1940. The Regiment spent the next 3 years on training and home defence duties. It moved to North Africa in March 1943 and then on to Italy in January 1944. 78 (Duke of Lancaster’s Own Yeomanry) Medium Regiment RA (TA) was re-organised as 78 Regiment RA (Auxiliary Police) in October 1945. It went into suspended animation in April 1946 and disbanded 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.
| Apr 40 | Formed | Haverfordwest, Pembrokeshire, UK | |
| Apr 40 |  |
Western Command | UK |
| Mar 41 |  |
4 Corps | South Coast, UK |
| Jan 42 |  |
Southern Command | UK |
| Dec 42 |  |
War Office control | UK |
| Mar 43 |  |
Middle East Forces | N Africa |
| Jan 44 |  |
8 Army | Italy |
| May 44 |  |
6 Army Group RA | Cassino, Italy |
| Oct 45 | Became 78 Regiment RA (Auxiliary Police) |
Batteries
| Apr 40 | A, B |
| Mar 42 | P, Q |
| Jan 43 | 105, 106 |
| Oct 45 | 105, 106, 700, 701, 702 |