In 1936, through his family doctor, he discovered that the Royal Air Force (RAF) was open to applications from men from the Dominions, reinvigorating his desire to fly.

Much of the squadron's training in peacetime involved formation flying and fighter tactics,[11] but Deere also played rugby for Rosslyn Park, a South London club.

[16] Within a matter of days, it was involved in the Battle of Barking Creek, when it was one of several squadrons scrambled in pursuit of aircraft detected by radar and two Hawker Hurricane fighters were shot down in a friendly fire incident.

On one such patrol Deere, directed by a controller, very nearly flew into a set of barrage balloons over Harwich and then ran into a perimeter fence when landing at a foggy Hornchurch.

[18][19] On 23 May Deere and Pilot Officer John Allen were detailed to escort Flight Lieutenant James Leathart, flying a Miles Master, a two-seat trainer, over to Calais to rescue No.

During this mission, and in sight of Leathart, Deere claimed his first combat victories, shooting down two of several Messerschmitt Bf 109s fighters that had approached while the Magister was still on the airfield.

[15][20][21] The action gave Deere an insight into the qualities of the Bf 109, which he considered "in the hands of a good pilot was a tough nut to crack.

Initially, it was faster in the dive, but slower in the climb; the Spitfire could out-turn but it was at a disadvantage in manoeuvres that entailed negative G forces [sic].

He hitched a ride on a British Army lorry to Dunkirk, and boarded a boat to Dover, then travelled via London to Hornchurch, where he had taken off some 19 hours earlier.

Later in the month Deere's award of the Distinguished Flying Cross (DFC) was announced, and was presented to him by King George VI at a ceremony at Hornchurch on 27 June.

[15][28] His citation for the DFC read: During May 1940, this officer has, in company with his squadron, taken part in numerous offensive patrols over Northern France, and has been engaged in seven combats often against superior numbers of the enemy.

As a result of the glancing blow with the Bf 109, the propeller blades of Deere's Spitfire were bent backwards, his cockpit hood partially stove in, the engine disabled, and much of the fin and rudder lost.

[31][32][33] The first phase of the Battle of Britain commenced on 10 July 1940, when Luftwaffe attacks on targets along the coast of England and on shipping were stepped up in the Kanalkampf (Channel war).

[44] On 12 August, Deere, while leading the squadron, pursued and shot down a Bf 109 that broke up his section's attack on a group of bombers off the Kent coast, near North Foreland.

[60] The published citation read: Since the outbreak of war this officer has personally destroyed eleven, and probably one other, enemy aircraft, and assisted in the destruction of two more.

In May 1941, the squadron provided air cover for the battleship HMS Prince of Wales, which was returning to Scotland after its involvement in the Battle of the Denmark Strait.

Although officially credited with this kill, his biographer, Richard Smith, considers it a possibility that this was in fact a friendly fire incident, and the aircraft destroyed may have been a Hurricane of No.

[74] By this time, high losses among fighter pilots and bomber crews saw the RAF reduce its offensive operations to Belgium and France over the winter months.

Arriving in early March, he taught American pilots fighter tactics learnt in the Battle of Britain and the later fighting over France.

[79][80] Due its losses, the squadron moved to Martlesham Heath to carry out convoy patrols and was scheduled for a rest period later in the month.

To his dismay, he found that Leigh-Mallory held him partially responsible for the losses due to his aggressive leadership and did not rescind his orders for the squadron to have a rest.

403 Squadron was based at Catterick;[81] it was still there in August, performing local patrols and working on practicing formation flying, when Deere was posted to the headquarters of No.

The latter had been an issue during the Battle of Britain, for the Luftwaffe's tactics of providing a close escort to bombers meant that fighters lost their advantage of speed.

[86] His first operation as wing leader was on 4 April 1943, escorting bombers to Abbeville, but he had to return prematurely when his Spitfire developed engine trouble.

On 4 June, Deere's award of the Distinguished Service Order (DSO) was announced,[88] the published citation reading: This officer has displayed exceptional qualities of skill which have played a large part in the successes of formations he has led.

341 Squadron, which was part of the Biggin Hill wing, had been killed in late August[94] and Checketts was shot down over France in early September although he was to make it back to England seven weeks later with the assistance of the French resistance.

[96][97] While on leave, and in recognition of his leadership of the Biggin Hill wing when it escorted bombers of the Eighth Air Force, Deere was awarded the Distinguished Flying Cross by the United States.

[100] On 1 May, at the request of the Chief of Staff of the Free French Air Force, Général de division (General) Martial Valin, Deere took command of No.

He also received a permanent commission, as a squadron leader, in the RAF on 1 September 1945,[111] although he continued to retain his acting wartime rank of wing commander.

[126] Promoted to air commodore in July 1964,[127] on 30 January 1965, he was given the honour of leading fellow Battle of Britain fighter pilots in the main funeral cortège for Winston Churchill at St. Paul's Cathedral.