| Unit Name: | 121st "Overseas" Battalion, CEF |
| Dates: | 1915–1917 |
| Disbanded: | 1917 |
| Country: | Canada |
| Branch: | Canadian Expeditionary Force |
| Type: | Infantry |
| Specialization: | --> |
| Garrison: | New Westminster |
| Garrison Label: | Mobilization headquarters |
| Nickname: | Western Irish |
| Colours: | --> |
| Colours Label: | --> |
| Battle Honours: | The Great War, 1916–17 |
| Commander1: | LCol Archibald Woodbury McLelan |
| Commander1 Label: | Officer commanding |
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[1] and began recruiting in that city. After sailing to England on [2] 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.[3]
The 121st Battalion is perpetuated by The British Columbia Regiment (Duke of Connaught's Own).[4] The perpetuation has been passed down through the following units as a result of reorganizations and amalgamations: