In 1916, as the First World War was raging in Europe, a 15-year old Roy ran away from home and enlisted in the South African Overseas Expeditionary Force. He used the assumed name of Roy McKenzie and claimed to be an 18-year old from Southern Rhodesia. However, a suspicious officer telephoned the Campbell family's home. Roy's sister Ethel picked up the phone and confirmed that Roy was only 15. Ethel later wrote, "This was the first that any of us knew of his having run away from school and joined up.