Thwaites was sufficiently impressed with Reilly's intelligence work in New York that he wrote a letter of recommendation to Mansfield Cumming, head of MI1(c). It was also Thwaites who recommended that Reilly first visit Toronto to obtain a military commission which is why Reilly enlisted in the Royal Flying Corps Canada. On 19 October 1917, Reilly received a commission as a temporary second lieutenant on probation. After receiving this commission, Reilly voyaged to London in 1918 where Cumming formally swore Lieutenant Reilly into service as a staff Case Officer in His Majesty's Secret Intelligence Service (SIS), prior to dispatching Reilly on counter-Bolshevik operations in Germany and Russia. According to Reilly's wife Pepita Bobadilla, Reilly was sent to Russia to "counter the work being done there by German agents" who were supporting radical factions and "to discover and report on the general feeling".