In February 1918 he was posted to the British Expeditionary Force (BEF), first at 1 Aeroplane Supply Depot at Saint-Omer in northern France, then with 58 Squadron at Clairmarais flying the FE.2b fighter/bomber. In March he moved to Auchel. In a census in April 1918 he is seen to have flown the DH.1, FE.2b and FE.2d.
After another move to Fauquembergues in April, Harold returned to England as a night flying pilot on the FE.2b at 4 Wing, Netheravon. He was with 12 Training Depot Station (TDS) at Netheravon in October, and was promoted to Lieutenant in November.
He returned to 58 Squadron in April 1919 flying the Handley-Page O/400 bomber. They became part of the Middle East Force (MEF) in April 1919 and Harold moved to Heliopolis in Egypt in May, converting to the Vickers Vimy bomber. He embarked at Suez in August for Mesopotamia and was with 58 Squadron at Baghdad in August “for duty in connection with aerial routes”. I assume that the RAF was doing survey duties for the opening of commercial air routes through the Middle East and India.
He embarked at Basrah for England in July 1920 and joined 207 Squadron at Bircham Newton in September. He was granted a Short Service Commission in October, and joined the Aeroplane Experimental Establishment at Martlesham Heath in January 1921
Flight magazine records his engagement to Muriel Joyce Durham on 3 March1921, just a week before his fatal accident when testing his DH10 F8423.
https://www.flightglobal.com/FlightPDFArchive/1921/1921%20-%200161.PDF
According to the second newspaper report, above, the crash happened at Gull Farm, Hasketon, which still exists.
Alan Smith, former archivist to the Martlesham Heath Aviation Society, has thrown new light on the subject from his records of events in the history of the airfield. He cites information from the Ipswich Records Office, the official inquest, and a post mortem report. According to this Harold's body was found at Bonds Close, Oak Tree Farm, Hasketon, just to the north of Gull Farm.
The inquest recorded that the aircraft was seen to be in difficulties at an altitude of about 500 feet, first falling then righting itself for a few seconds, then crashing to earth.
The accident was witnessed by Walter Thorpe, of Bonds Farm, who found the deceased lying beside the machine. After seeing the body at the mortuary at Martlesham airfield, medical officer Flight Lieutenant Alfred Parkes stated that there was a dislocation of the neck and other serious injuries, leading to instantaneous death.
David G. Bett, a farmer at Haskerton stated :
"Yesterday, Thursday morning, I saw an aeroplane flying overhead. The plane seemed to be flying all right except that it appeared to be going rather slowly for a big plane. It did not seem to be making as much noise as usual. As it came towards me one wing seemed to lift slightly once or twice. The plane was coming down wind, turned left handed and then suddenly made a spinning dive. I thought it must crash but it recovered and got onto an even keel and I thought it was alright. In about 5 seconds or so, however, it nose dived straight to the earth. I went directly, as quickly as I could. I found several people there and a couple were searching the wreckage in case there might be another victim."
Flight Lieutenant Edmund May Pizey, from RAF Martlesham Heath, stated that Harold Gardner had been stationed there for about six weeks. He was quite capable of handling the machine, and had considerable experience on twin-engined aircraft. Flight Lieutenant Pizey had flown the same machine twice that week and had no trouble with it. He was present when Flying Officer Gardner took off at about 10.45 am. The engines were tested satisfactorily on the ground before he left. He had not complained of any illness or feeling unwell before he flew and was normal and cheerful. He was very keen on flying that machine.
It would be of interest to know if there are local records of the event, and whether any remains of wreckage were preserved.