He was assigned No. 11 Squadron, the first British flying squadron to be equipped with a purpose-built fighter aircraft, the pusher Vickers Gunbus. The squadron arrived in France on 25 July 1915, at approximately the time Adolphe Pegoud became the first ace in history. Three days later, Hargreaves scored his first aerial victory while teamed with Rees in Gunbus Serial No. 1649, driving a Fokker Eindekker down out of control. On 31 August, they destroyed an LVG two-seater reconnaissance plane. Hargreaves' third victory came on 21 September, when he drove down an AGO reconnaissance aircraft over Herbecourt. The next day, he repeated the feat, driving down an Albatros two-seater south-east of Albert. On the 30th, they forced down another Albatros, this one from the German artillery cooperation squadron, Feld-Flieger-Abteilung 23. The dying crew crash-landed behind British lines, and the aircraft was captured.
