In September 1914, Cunnell enlisted as a private, and soon was promoted to sergeant. and saw active service on the
Western Front. On 24 November 1916 he was seconded for duty with the
Royal Flying Corps, and appointed a temporary flying officer. On 1 March 1917 he was promoted to lieutenant. On 14 May 1917 Cunnell was appointed a
flight commander with the temporary rank of captain. Between 2 May and 11 July, Cunnell claimed nine victories (five claimed destroyed, four "out of control") flying a
FE2d with
No 20 Squadron. after his forced landing On 6 July 1917, Cunnell, flying with Second Lieutenant Albert Edward Woodbridge, was part of a patrol of six aircraft attacked by a flight of German
Albatros D.Vs including one flown by
Manfred von Richthofen. During the clash Richthofen was wounded in the head and forced to land near Wervicq. The victory was credited to the crew of Cunnell's A6412. It is often falsely stated that this was the only time Richthofen was shot down in air-to-air combat, overlooking
Edwin Benbow's victory over the Red Baron on 6 March 1917. However, this was the only time the Red Baron was wounded in action. Woodbridge later described the action: Richthofen's subsequent medical treatment disclosed that the bullet that hit him may have come from behind. Despite Cunnell and Woodbridge's confirmed claim for this aerial victory, Richthofen may have fallen from fire from one of the other FE.2s of 20 Squadron, from being shot down by
Raymond Collishaw, or even from one of Collishaw's wingmen from 'B' Flight,
10 Naval Squadron such as
William Melville Alexander,
Ellis Vair Reid, or
Desmond Fitzgibbon. Cunnell was killed by German anti-aircraft fire a few days later on 12 July 1917, near
Wervicq, Belgium; his observer, Lt. A. G. Bill, successfully flew his fighter back to base. He was buried at the Bailleul Communal Cemetery Extension North at
Bailleul,
France, close to the
Belgian border, in grave number III.C.263. ==War record==