Nation was commissioned a second lieutenant in the Royal Engineers on 1 April 1895, and promoted to lieutenant on 1 April 1898. He served in the Second Boer War in South Africa from 1899 to 1902. He was first posted in the Orange Free State, including engagements at Vet River and Zand River; later in the Transvaal, where he was present at actions near Johannesburg and Pretoria, including the battles of Diamond Hill (June 1900) and Belfast (August 1900); and eventually in Cape Colony, south of the Orange River. Following the end of the war in June 1902, he left Cape Town for England on the "SS Moravian" in August 1902. He was stationed in Buncrana in 1903.