Two served with the Canadian Expeditionary Force (CEF) during First World War.
The last prime minister to serve in the military was Pierre Trudeau, who joined the Canadian Officers' Training Corps during the Second World War.
The prime ministers with military experience have only served with the land forces of Canada, the active militias/Canadian Army,[note 1] or the CEF.
Lester B. Pearson is the only prime minister to serve in the British Army, having transferred to the Royal Flying Corps from the CEF.
[note 2] The prime minister is not commander-in-chief of the Canadian Armed Forces, rather the role is held by the monarch of Canada and is held on behalf of the monarch by the governor general of Canada.