The 91st Battery was authorized to moblilize on the 3rd September1939, and recruited to full strenght in the first two weeks of the war. Training was carried out at Mewata Armouries and rows of guns became a familiar sight along the C.P.R siding on Ninth Avenue. In January 1940, the battery ,moved tob the Prince of Wales Armouries in Edmonton where it remained until May when it moved to Camp Shilo, Manitoba, and became part of the 6th Canadian Field Regiment. Intensive training was carried out here until August 20th when the Regiment for overseas. On 5th September 1940, the Battery landed at Glasgow and the following day was settled in Lille Barracks, aldershot, where it remained for 11months carrying out training. During this time the unit became part of the Anti Invasion Force. It was also during this period that the Battery suffered its first casualties due to enemy action, two men being killed when the Officers Mess suffered a direct hit during an air raid on the night of 11 January 1941.

In August 1941, the Battery took up defence duties on the south coast of England, going first into the Seaford area and for the following three years almost every town and village on the south and southeast coast became familiar with the 2nd Division 44 Tactical sign. In the winter of 43-44 the 91st Battery, with the remainder of the Regiment moved into a concentration area in the vicinity of Worthing and the next step took them to Tilbury Docks where they waited to embark for the continent. On the 6th July 1944, one month after D.Day the Battery landed on the continent and went into action. They were present at Caen, Falaise, and the Carpiquet airport and took part in the break-through across France, Belgium and into Holland.

The winter of 1944 saw the unit in Nijmegen where it stayed with the remainder of the 2nd Division until the spring offensive. From Nijmegen it pushed south into Germany, across the Siegfried Line and helped clear out of the Reichswald and Hochwald forests, up to Xanten and the west banks of the Rhine. At Easter 1945, the rhine was crossed and the Battery did its part in the thrust across Germany towards Oldenburg. By this time this push was completed Germany capitulated and the Battery moved into its pre-occupational role in the Oldenburg area. Clean-up and Police duties were carried out from then until the Canadian Occupational Force took over.

At an historic ceremony on Dutch soil the Regiment turned in its guns and equipment and settled down to garrison duties until its turn to move into Nijmegen area and thence to England for reparitation home.