Kain began flying operational sorties during the Phoney War and gained his first aerial victory, a German bomber, in November 1939.

On 7 June 1940, having bid farewell to his squadron and in a gesture to his comrades, he took off in a Hurricane to perform a series of low-level aerobatics over Échemines airfield.

He also received tuition in mathematics from Professor George William von Zedlitz of the Victoria University of Wellington; this was necessary after his failure to graduate from secondary school as such academic qualifications were prerequisites enter the RAF as a pilot.

Accordingly, having convinced his parents to support his endeavours, Kain departed New Zealand in November 1936, accompanying his father on a business trip to England aboard the RMS Orford.

[5] Once in London, Kain formally applied to the Air Ministry for a short-service commission in the RAF but failed his medical due to high blood pressure.

[7] On completion of the elementary course on 5 March 1937, Kain was accepted for a short-service commission with the rank of acting pilot officer and the service number 39534.

[14] He continued to develop his aerobatic skills with the Gladiator and in May 1938 took part in the Empire Air Day, giving flying demonstrations to the public.

[22] On 10 September 1939, Kain flew his first operational patrols, covering ships disembarking the BEF at Cherbourg, without making contact with the enemy.

60 Mobile Wing was attached to the Advanced Air Striking Force (AASF), comprising several squadrons of Fairey Battles of Bomber Command.

The event was widely reported although, due to the RAF prohibition of the naming of its personnel in the media, Kain was not identified as the successful pilot in British newspapers.

[36] Kain spent some of this period in England on leave with Joyce Phillips,[37] a theatre actress he had met while completing his flight training in 1937.

[39] The weather still permitted occasional patrols; in late January his flight encountered a Heinkel He 111 medium bomber but Kain's guns failed to fire.

[41] By early February 1940 the thaw was well underway, but this affected the runway of the aerodrome which was prone to bogging, impacting flight operations for the next few weeks.

[Note 2] Over the German lines when the attack took place, Kain glided 30 miles (48 km) from 20,000 feet (6,100 m) to reach French territory.

When his damaged engine caught fire, Kain prepared to bail out but had to re-enter the cockpit when he realised his parachute strap was not in position.

[46] In mid-March he was informed of his impending award of the Distinguished Flying Cross (DFC), in recognition of the action earlier in the month when he had shot down his first Bf 109.

Thick smoke and oil fumes had filled his cockpit and although unable to see his compass, he skilfully piloted his aircraft inside allied lines in spite of being choked and blinded by the smoke.With the announcement of his DFC, the anonymity he had previously been afforded was no longer possible.

Tensions were high as a result of the German invasions of Norway and Denmark, and the Luftwaffe had increased its presence along the French border with Germany.

While escorting some Fairey Battles on a raid north of Sedan, Kain spotted a Henschel Hs 126 reconnaissance aircraft that he pursued and destroyed over Bouillon.

[73] The next day, the squadron moved to Villeneuve while Kain led his flight in a covering patrol to help protect the shift to the new base.

[76] The next day, the entire squadron took part in a defensive patrol during which it met a group of German bombers, He 111s and Ju 88s, with an escort of Bf 110 fighters.

That day he led a section in a morning patrol, during which he destroyed a Do 17 but had to then make an emergency landing back at Gaye due to damage inflicted on his Hurricane by machine-gun fire from the bomber's rear gunner.

[83] The situation in France was now deteriorating; the French army was defending the line along the Somme and Aisne with the fighter squadrons of the AASF operating in support,[82] while the BEF was being evacuated from Dunkirk.

It was the subject of a bombing raid during which Kain met Ginger Lacey, who later became one of the RAF's highest scoring flying aces of the war.

[86] He resumed flying on 31 May, leading a section in an uneventful mission providing cover for Fairey Battle bombers attacking German forces southeast of Reims.

[87] Kain led a flight of Hurricanes there early in the morning of 3 June; they then covered the move of the ground crew and administrative staff to Le Mans.

A group of pilots arrived the next day for allocation to units of the AASF; four were assigned to Kain's squadron, freeing him to return to England.

[90] In front of a group of his squadron mates who gathered at the airfield at Échemines to bid him farewell, he took off in his Hurricane to fly to Le Mans to collect his kit.

[96] As the RAF's first recipient of the DFC and its first flying ace of the war, Kain had a high profile in Britain and the Dominions and his death was widely covered in newspapers.

[97][101][102] Aviation historians Christopher Shores and Clive Williams credit Kain with 16 aircraft destroyed and 1 damaged, [103] as does author Mike Spick.