In November 1916 Hoidge attached to the Royal Flying Corps, as a second lieutenant. He was posted to No. 56 Squadron to fly a Royal Aircraft Factory SE 5 fighter in 1917. The S.E.5a was extremely popular with Allied pilots and became the plane used by Mick Mannock, Billy Bishop and James McCudden. The S.E.5a was fast, manoeuvrable at high altitude and easy to fly.
Hoidge's first victory was over an Albatros D.III on 5th May 1917 over Montigny le Bretonneux. On 5th June, he helped bring down, Karl Emil Schäfer, one of Germany's most important pilots. He was awarded the Military Cross on 18th July: "For conspicuous gallantry and devotion. On many occasions he has attacked and destroyed or driven down hostile machines, and has taken part in twenty-four offensive patrols. In all combats his bravery and skill have been most marked."
Hoidge joined with James McCudden, Arthur Rhys-Davids, Richard Maybery, Geoffrey Hilton Bowman and Keith Muspratt, in shooting down Werner Voss, a leading German Ace, who had at this point had 48 victories, on 23rd September, 1917. Hoidge's final total included 23 successes over enemy fighters and five over opposing two-seater reconnaissance planes.
He was painted by William Orpen soon after this action took place. Orphen later recalled in his book, An Onlooker in France (1921): "Hoidge had also brought down a lot of Germans. His face was wonderfully fitted for a man-bird. His eyes were bird's eyes. A good lad was Hoidge, and I became very fond of him afterwards."
Reginald Hoidge died in New York City on 1st March 1963.
General Trenchard and Maurice Baring chose out two of the leading flying boys for me to paint, and they sat to me at Cassel. One was 2nd Lieutenant A.P. Rhys Davids, DSO, MG, a great youth. He had brought down a lot of Germans, including two cracks, Schaffer and Voss. The first time I saw him was at the aerodrome at Estre Blanche. I watched him land in his machine, just back from over the lines. Out he got, stuck his hands in his pockets, and laughed and talked about the flight with Hoidge and others of the patrol, and his Major, Bloomfield. A fine lad, Rhys Davids, with a far-seeing, clear eye. He hated fighting, hated flying, loved books and was terribly anxious for the war to be over, so that he could get to Oxford. He had been captain of Eton the year before, so he was an all-round chap, and must have been a magnificent pilot. The 56th Squadron was very sad when he was reported missing, and refused to believe for one moment that he had been killed till they got the certain news. It was a great loss.
The other airman chosen was Captain Hoidge, MC and Bar - "George" of Toronto. Hoidge had also brought down a lot of Germans. His face was wonderfully fitted for a man-bird. His eyes were bird's eyes. A good lad was Hoidge, and I became very fond of him afterwards. I arranged with Maurice Baring and Major Bloomfield that Hoidge was to come to Cassel one morning at 11 am to sit to me. The morning arrived and ii o'clock and no Hoidge. 11.30, 12 - no Hoidge. About 12.30 he strolled into the yard and I heard him asking for me in a slow voice. I was raging with anger by this time. He came upstairs and I told him there was no use doing anything before lunch, and that we had better go down and get some food. We ate silently. I could see he was rather depressed. About half-way through our meal, he said: "I'm lucky to be here with you this morning!" "Why?" said I. "Oh," he said, "I made a damned fool of myself this morning. Let an old Boche get on my tail. Damned fool I was - with my experience. Never saw the blighter. I was following an old two-seater at the time. He put a bullet through the box by my head, and cut two of my stays. If old B. hadn't happened to come up and chased him off I was for it. Damned fool! But the morning wasn't wasted, afterwards I got two two-seaters." I said: "Do you realise you have killed four men this morning?" "No," he said, "but I winged two damned nice birds." Then we went upstairs and he sat like a lamb.