From Sandhurst, Frederick was commissioned a second lieutenant in the Royal Fusiliers on 11 February 1899. He fought with the 2nd battalion in the Second Boer War and was present at the battles of Colenso (December 1899) and the Tugela Heights (February 1900), leading to the Relief of Ladysmith (1 March 1900), following which he was promoted to lieutenant on 16 March 1900. Serving in the Transvaal in 1900, he stayed in South Africa throughout the war which ended with the Peace of Vereeniging in June 1902. Four months later he left Cape Town on the SS "Salamis" with other officers and men of the battalion, arriving at Southampton in late October, when the battalion was posted to Aldershot.