On 26 April 1917 he applied to join the Australian Flying Corps, and on 1 May was appointed a second lieutenant in the AIF, allotted to the AFC. Gordon began pilot training at RAAF Point Cook, which he was unable to complete for medical reasons. However, on 21 June Gordon embarked aboard HMAT "Suevic" (A29) at Melbourne, and sailed for England, arriving at Liverpool on 26 August. On 4 September Gordon was posted to the AFC Depot at Halton Camp, and on 28 December was appointed a flying officer (observer).