Here is some information on the battalion Dick Armer joined. It was known as the142nd Battalion (London's Own)
Stewart reports that the 142nd Battalion was organized on December 22, 1915, with a strength of 574 men. The unit was disbanded after the Great War on September 15, 1920. The 142nd Canadian Infantry Battalion was absorbed by the 23rd Reserve Battalion  to provide reinforcements for the Canadian Corps in the field. The 142nd Battalion is affiliated with the 1st and 33rd CEF Battalions and is perpetuated by the 3rd Battalion of the Royal Canadian Regiment (RCR) "London and Oxford Fusiliers" of the Canadian Army Militia. During the Great War the 142nd Battalion (due to men serving in other active battalions) received "Battle Honours" at Ypres 1915-17; Gravenstafel; St. Julien; Festubert 1915; Mount Sorrel; Somme 1916; Pozières; Flers-Courcelette; Ancre Heights; Arras 1917-18; Vimy 1917; Arleu; Scarpe 1917-18; Hill 70; Passchendaele; Amiens; Drocourt-Queant; Hindenburg Line; Canal du Nord; Pursuit to Mons; France and Flanders 1915-1918.
Lieutenant George Van Wyck Laughton, M.C. (Vimy Ridge)  of the 7th Regiment Fusiliers (Militia) attested to the 142nd Canadian Infantry Battalion in 1915. Details of the links between the Militia and the Canadian Expeditionary Force are provided on Lt. Laughton's web site.
ReferencesMeek, John F. Over the Top! The Canadian Infantry in the First World War. Orangeville, Ont.: The Author, 1971.
Stewart, Charles H. "OVERSEAS - The Lineages and Insignia of the Canadian Expeditionary Force 1914-1919. Little & Stewart, Toronto ON, 1970.
Canadian Expeditionary Force MATRIX PROJECT 
Come back tomorrow for Dick's first letter home from Camp Borden