On 13 November 1914, Randall was among cadets and ex-cadets of the Officers' Training Corps appointed as temporary second lieutenants in the infantry. After serving in a reserve battalion of the Border Regiment, he was attached to the Royal Flying Corps on 27 October 1916, and appointed a flying officer, transferred to the General List, on 30 November. He was posted to No. 32 Squadron, flying an Airco DH.2. He scored his first aerial victory with them on 23 January 1917. He would score one more win with them, being wounded in the process, on 11 March 1917. On 1 April 1917 he was promoted to lieutenant, and on 3 June was appointed a flight commander with the temporary rank of captain. His second combat tour was as a fighter pilot with No. 85 Squadron, flying a Royal Aircraft Factory SE.5a. This time around, he scored another eight aerial victories, between June and October 1918, culminating in the award of the Distinguished Flying Cross just days before the Armistice. His citation read: