[2] Ritson joined the British Army as a young man and in 1906 he was made second lieutenant in the Durham Light Infantry.
[2][4] Ritson's career as an inspector of mines was placed on hold when he was called for active service with the outbreak of the First World War, where as a former soldier he was recalled to the Durham Light Infantry serving in the Territorial Army.
[5][6] Ritson took over the post at Imperial College from Professor S. J. Truscott, who had desired that the department focus more on coal and iron mining.
[7] Ritson remained at Royal School of Mines until 1952 when he was succeeded by J.C. Mitcheson, and in 1955 he was made a fellow of Imperial College in recognition of his work.
[9][10] In 1908 Ritson was approached to join and Anglo-Welsh team, a fore-runner of the British and Irish Lions, to tour Australia and New Zealand.
[1] A seven-month tour, run on a strictly amateur basis, would suggest that Ritson was independently wealthy to accept a place on the team.
One of eight new caps, Ritson experienced his first international win as England overcame a strong French performance to take the match 11–3.
As in his previous two encounters Ritson finished on the winning side as a strong English first half turned into a rout as the French team disintegrated to lose 20–0.
The game was dominated by strong defensive play from both teams which resulted in just a single score, an England try from prop Bruno Brown.
[20] On 15 April 1917 he was placed in charge of the 12th Battalion of the Scots Guard, replacing Lieutenant Colonel Harold Underhill Hatton Thorne, who had been killed at the Battle of Arras.
[2] Ritson was the commanding officer of the 12th Battalion at Zonnenbeke, when on 20 September 1917 he was charged with clearing out several strongpoints which included five pillboxes and a fortified farmhouse.