[3] Harrison came to note as a rugby player when he represented the Royal Marine Artillery team based in Woolwich.
An imposing forward player, he was selected for both the Army and Royal Navy teams before representing the United Services.
The United Services was made up of servicemen from the Royal Navy and played against the biggest clubs from all over Great Britain.
England had won the opening game of the tournament against Wales, and Harrison retained his place when they narrowly beat Ireland at Twickenham.
Harrison was given conversion duties during the match, an unusual tactic for a forward, and successfully kicked two goals which prove decisive in a narrow 16–15 win for his England team.
Harrison continued to play rugby during the war, and again captained the Barbarians in a 1915 encounter with a South African Services XI.
[9] During the First World War he was initially stationed in German South-West Africa, where he served as a commander of a South African siege battery.
[12] He returned to active duty in October 1918, and served in the Heavy Artillery division of the XI Corps at the Western Front.
[12] He transferred from the Royal Marines to the British Army's East Yorkshire Regiment in 1924 and was brevetted lieutenant colonel in 1927.
He served in Singapore from March 1923 until April 1924, where he was General Staff Officer Grade 3 (GSO3) before being posted to British Malaya until 1925 as GSO 2.
[16] For his services whilst in the military Harrison was awarded the Order of the Sacred Treasure of Japan in 1926 and the Companionship of the Bath in 1939.