Cap badge The King's Own Calgary Regiment (RCAC) (1925 issue), 3rd Canadian Division

The overseas unit trained on various vehicles in Canada and the United Kingdom, and in August 1942 took the Churchill tank into battle for the first time at Dieppe. The unit was rebuilt after the raid, having left large numbers of tanks and crews behind. A notable casualty was Lieutenant Colonel "Johnny" Andrews, who was killed in action.

In the spring of 1943, Lieutenant-Colonel C.H. Neroutsos took command of the regiment. The new unit went to Sicily in 1943 with the 1st Canadian Army Tank Brigade, re-equipped with the Sherman tank.

On 3 September 1943, the regiment assaulted the beaches of Reggio Calabria to little resistance and moved northwards with notable engagements in Potenza, Mottaand Campobasso while supporting the 1st Canadian Infantry Division. On 21 November 1943, the regiment supported the 8th Indian Infantry Division in its assault against fierce German opposition on the Sangro River. In December the regiment met stubborn opposition fighting for the Moro River and later Vino Ridge and the Ortona Crossroads.

On 11–12 May 1944 the regiment assaulted across the Gari River supporting the 19th Indian Brigade of the 8th Indian Division. During this operation and the advance towards the Hitler Line the regiment sustained casualties numbering 16 officers, 40 other ranks, and 60 tank casualties. An innovative use of a modified Sherman tank to carry a bridge across the Gari River is known as Kingsmill bridge by its inventor Captain T. Kingsmill's moniker. Kingsmill was to receive the Military Cross for the action. At this point Lieutenant-Colonel Neroutsos fell ill, and the regiment was taken over by Lieutenant-Colonel C.A. Richardson.

In June 1944 the Calgaries took part in the Battle of Lake Trasimeno in support of the British 4th Division, after which the Calgaries conducted a pursuit up the Chiani Valley until the Lydia Line was reached south of Arezzo. By 3 August 1944, the regiment had advanced with the 8th Indian Division to the Arno River through country with remarkably poor tank going.

On 25 August 1944 the Calgaries made an assault crossing of the Arno River, east of Florence pushing into the Sieve Valley where the Gothic Line was assaulted in the "Marradi" sector in support of the 1/5 Gurkha Regiment. Another miserably wet Italian winter was spent in the mountains.

In late February 1945 the regiment was moved to Leghorn and embarked to Marseilles, France, where it moved by rail to the North-West Europe theatre. The regiment moved to the Reichswald Forest and on 12 April 1945 fought in the Second Battle of Arnhem, supporting the 49th (West Riding) Infantry Division to Ede, the Netherlands. The regiment's final actions of the Second World War were in support of the 1st Belgium Brigade in clearing the resistance between the Nederrijn and Waal Rivers.

When the overseas unit returned to Canada in 1945, it was disbanded, and the Calgary Regiment continued its service as a reserve armoured unit.