On 20 August 1914 Gordon enlisted into the 10th Battalion at Morphettville, South Australia. On 28 August, on account of his previous military experience, he was promoted to the rank of acting sergeant, and this was confirmed on 1 September. On 20 October the 10th Battalion sailed from Adelaide aboard HMAT "Ascanius" (A11) eventually disembarking in Egypt. After further training the battalion sailed as part of the 3rd Brigade to the Greek island of Lemnos in early March 1915. Gordon, with the rest of 3rd Brigade, sailed from Lemnos on 24 April 1915, landing at Anzac Cove at Gallipoli early the following day. As a sergeant in No. 1 Section, No. 1 Platoon, "A" Company, Gordon served as a Battalion Scout and was amongst the first men ashore. He was transferred to the Machine Gun Section at the end of June, and was commissioned as a second lieutenant on 4 August.