Patricia's were mobilized for active service on 1 September, 1939.  Recruited in Winnipeg and on Vancouver Island, the Battalion was brought up to strength in October and concentrated in Winnipeg under the command of LCol W.G. (Shorty) Colquhoun, MC.  The Regiment sailed from Halifax on 21 December, 1939, in the ORAMA as part of the 1st Canadian Infantry Division.

On arrival in Scotland, the Regiment moved to Aldershot Command and spent New Year's Eve in Cove, England.  Immediately upon arrival in England, LCol  Colquhoun reported to the Colonel-in-Chief at Bagshot Park.  On 10 February, 1940, the Colonel-in-Chief inspected her Regiment for the first time in 21 years.

The Regiment spent three years in the United Kingdom, most of which was spent in coastal defence and training in various parts of the country.

On 10 July, 1943, 1st Canadian Infantry Division landed in Sicily as part of the 8th Army. The Patricia=s were re-indoctrinated to war at Leonforte, our first WWII Battle Honour.  Following the capture of Sicily by the Allies, the Regiment landed on Italy=s Atoe@ on 4 September 1943.  The first two months were spent advancing inland (northward) with the Regiment=s progress slowed by demolished bridges and German rear guards.  During December >43, the Patricia=s were heavily involved in the operations of Villa Rogatti and the Gully, winning many individual and unit honours in the process, and spent Christmas in Ortona.  The next major offensive came at the Hitler Line, west of Monte Cassino, in late May >44 during the Allied advance to Rome. Towards the end of August, the Regiment moved back to the Adriatic and took part in the assaults on the Gothic Line, San Fortunato and Rimini.  The rugged terrain and seemingly never ending river crossings had taken their toll; both in men and equipment.  

Over the next five months, the Patricia=s campaigned yet further north, in the Romanga, a wide valley crossed by numerous small and medium sized waterways, winning three more Battle Honours in the process.  It was during the Italian Campaign that the Regiment renewed its traditions of professionalism, tenacity and aggressiveness that it demonstrated so aptly in WWI.  The Italian Battle Honours on the colours show proof of the sacrifices made and victories gained by the rank and file of the Regiment.  The Patricia=s embarked enroute to North West Europe on 13 March, 1945.

Travelling on a scenic, non battle scarred route through southern and central France, the Regiment made its way to Boisschot, Belgium.  Following eleven days of light activity, the Regiment was again on the move with 1st Canadian Division to liberate Holland, and on April 11th, co-leading the divisional crossing of the Ijssel River, played an important part in the capture of Apeldoorn.  The Patricias, having stood fast in Barneveld, were on hand as security and logistical organizers for the historic Achterveld Conference between the Allies and the Germans on April 30th.  Victory in Europe (VE) Day was 5 May 1945, and on 7 May, LCol Clark and his  Patricia=s and were the first Allies in Amsterdam.

The Regiment had fought throughout World War II as part of the 2nd Brigade with its old friends and worthy comrades, The Loyal Edmonton Regiment (formerly 49th Battalion) and the Seaforth Highlanders of Canada from Vancouver, who share many similar Battle Honours.

On 1 June, 1945, a new battalion of the Regiment was authorized to form part of the Canadian Pacific Force in the campaign against Japan.  Its official designation was 1st Canadian Infantry Battalion, Princess Patricia's Canadian Light Infantry, 2nd Canadian Infantry Regiment.  The Battalion assembled at Camp Shilo and then moved to Camp MacDonald for training.  After the destruction of Hiroshima and Nagasaki by atomic bombs and Japan's subsequent surrender on 15 August, 1945, the Pacific Force was disbanded.  Until a decision was reached to form a Permanent Force, the holding establishment was named the "Interim Force".  Due to this change, the new battalion was redesignated on 2 September, 1945, as 2nd Battalion, Princess Patricia's Canadian Light Infantry, Canadian Infantry Corps.  In the meantime, the Regiment's battalion in Europe, very much under strength, returned to Winnipeg in October, 1945, and was demobilized.