In early 1913, after discussions with some of his fellow doctors, Chavasse applied for and was accepted by the Royal Army Medical Corps (RAMC); he was commissioned as a lieutenant on 2 June. Thanks to one of his mentors, Dr McAlistair, who was then Surgeon-Captain of the 10th Battalion of the King's (Liverpool Regiment), the Liverpool Scottish, he was attached to the battalion as Surgeon-Lieutenant. The 10th Kings had been a Territorial battalion since the Haldane Reforms in 1909. Chavasse joined the battalion on 2 June 1913 and was welcomed by Lieutenant-Colonel W. Nicholl, the commanding officer. As an officer in a Territorial unit, Chavasse now had to attend to both his civilian and military duties.