Details from the regiment were called out on service before the actual start of the war on 26 August 1939 and placed on active service on 1 September 1939 as The Argyll and Sutherland Highlanders (Princess Louise's) (Machine Gun), CASF (Details), for local protection duties.
The details were formed as a battalion and designated The Argyll and Sutherland Highlanders (Princess Louise's), CASF on 15 August 1940. It was redesignated the 1st Battalion, The Argyll and Sutherland Highlanders (Princess Louise's) (Machine Gun), CASF on 7 November 1940 and then the 1st Battalion, The Argyll and Sutherland Highlanders (Princess Louise's), CASF on 1 February 1941. It served in Jamaica on garrison duty from 10 September 1941 to 20 May 1943, and embarked for Great Britain on 21 July 1943. On 26 July 1944, it landed in France as part of the 10th Infantry Brigade, 4th Canadian Armoured Division, and it continued to fight in North West Europe until the end of the war. The overseas battalion was disbanded on 15 February 1946.
The Argylls mobilized a battalion for the Canadian Active Service Force in June 1940. Prior to this, there were occasional call outs. Beginning in August 1939, Argylls performed guard duty on the local canal and electrical facility, for example. The problems of active duty were myriad. First World War pattern tunics and the kilt were issued until modern Battle Dress was issued, Ross rifles were the only weapons, and hollow pipes and bricks comprised heavy weapons for the mortar platoon.
- Niagara
The first months of the war were spent in and around Niagara-on-the-Lake, a dreary round of guard duty on the Welland Canal and local power facilities. There was little training and almost no new equipment. The first Bren light machine guns, for example, arrived in December 1940. But there was time for setting the foundations for excellent administration and for addressing the usual range of problems associated with turning civilians into soldiers. It was during this period that the notorious "Mad Five" went AWOL, made their way to the Sunnyside amusement park in Toronto and telegraphed the CO — "Having a great time. Wish you were here." In May 1941 the 1st Battalion entrained for Nanaimo, B.C., where it underwent several tedious months of route marches alternating with inspections.
- Jamaica
September 1941 to May 1943 brought a sojourn in the sun — garrison duty in Jamaica. During this period, the reality of war was brought home by the fate of the Winnipeg Grenadiers (which unit the Argylls replaced in Jamaica) in Hong Kong, and of the Royal Hamilton Light Infantry (a sister unit from Hamilton) at Dieppe. Under the command of Lieutenant Colonel Ian Sinclair, the unit received new weapons and modern equipment, improved its administration, and began a complete program of small unit tactics, fitness, and training.
- England
The men of the 1st Battalion returned to Hamilton in May 1943. In preparation for overseas service, it received a new CO and senior officers, and many warrant officers and NCOs were also replaced. A notable exception was the Regimental Sergeant Major, Peter Caithness McGinlay. By August 1943 the unit had moved to England and joined the l0th Brigade of the 4th Canadian (Armoured) Division. Acting Sergeant John Rennie won a posthumous George Cross in October 1943, dying while shielding others from an exploding grenade during training. Collective training, specialized courses for individuals, and schemes at battalion, brigade and divisional level occupied the unit, now under the command of Lieutenant Colonel J. David Stewart for whom the Argylls' reported a genuine affection. In action, he was described as having an intuitive sense of battle (which could not be taught), cool imperturbability, and a refusal to fight according to preconceived notions.
- Normandy
The unit's first battles in early August 1944 were small successes fought along the road to Falaise. The first major action, Hill 195 on 10 August, was an unorthodox success; Stewart led the Battalion single file through the darkness of night and German lines to capture this hitherto unassailable strong point. It was an act which historian John A. English has called "the single most impressive action of Operation Totalize." Less than ten days later in the Falaise Gap, a battle group of "B" and "C" companies of the Argylls, and a squadron of South Alberta Regiment tanks captured St Lambert-sur-Dives and held it for three days against desperate counter-attacks. The action resulted in Major David Vivian Currie of the South Albertas being awarded the Victoria Cross.