During the First World War, the Regiment acted as a training unit providing 145 officers and 5,207 other ranks for service in the numbered battalions of the C.E.F., especially the 16th, 19th, and the 173rd Highlanders. The latter was broken up for reinforcements, much to the chagrin of its men. Although the Argylls perpetuate both the 19th and the 173rd, it is the former which provides the Regiment its most intimate connection with the Great War. The 91st gave the 19th all four of its commanding officers and its Pipe Major, Charles Davidson Dunbar, DCM, a Pipe Major of international renown.
As part of the 4th Infantry Brigade, 2nd Division, the 19th went from the mud and misery of Salisbury Plain, England, to the mud and blood of Flanders. The Battalion saw its first action at Saint-Eloi in April 1916 and went on to serve on the Somme, at Courcelette, Vimy Ridge, Hill 70, Passchendaele, Drocourt-Quéant, and the Pursuit to Mons. In December 1918, its pipe Band played a victorious Canadian Corps across the Rhine and into Germany. The 19th has had no official history published.