The 121st (Western Irish) Battalion, CEF was a unit in the Canadian Expeditionary Force during the First World War. Based in New Westminster, British Columbia, the unit was authorized on 22 December 1915 and began recruiting in that city. After sailing to England on in August 1916, the battalion was absorbed into the 16th Reserve Battalion on January 10, 1917. The 121st (Western Irish) Battalion, CEF had one Officer Commanding: Lieutenant-Colonel Archibald Woodbury McLelan.

The 121st Battalion is perpetuated by The British Columbia Regiment (Duke of Connaught's Own).Canadian Forces Publication A-DH-267-003 Insignia and Lineages of the Canadian Forces. Volume 3: Combat Arms Regiments. The perpetuation has been passed down through the following units as a result of reorganizations and amalgamations:

1920–1936: 1st Battalion (121st Battalion, CEF), The Irish Fusiliers of Canada 1936–1946: Irish Fusiliers (Vancouver Regiment) 1946–1958: 65th Light Anti-Aircraft Regiment (Irish Fusiliers), RCA 1958–2002: The Irish Fusiliers of Canada (The Vancouver Regiment) 2002–present: The British Columbia Regiment (Duke of Connaught's Own)

References Meek, John F. Over the Top! The Canadian Infantry in the First World War. Orangeville, Ont.: The Author, 1971.