Boulton Paul Defiant

The 1930s saw rapid developments in aircraft design. Most significant was the appearance of the monoplane, and especially the monoplane fighters with their greatly increased speed. This produced a great deal of uncertainty about the future of aerial combat, including a belief that these greatly increased speeds would make fighter dogfights almost impossible.

One product of this uncertainty was the Boulton Paul Defiant turret armed fighter. It was believed that fire from a powered turret would be more accurate than that provided by fixed forward firing guns. The turret would also have the advantage of a wider field of fire, and would reduce the stress on the pilot.

Boulton Paul Defiant I side plan
Boulton Paul Defiant I side plan

Boulton Paul Defiant prototype with no turret
Boulton Paul Defiant prototype with no turret

Boulton Paul was one of the first British companies to get involved in the production of powered gun turrets, having developed a nose turret for their own Sidestrand bomber (the resulting aircraft was known as the Overstrand). In 1935 they had acquired the rights to manufacture and develop a turret designed by the French engineer J. B. A. de Boysson. This was a fully enclosed turret, powered by a hydraulic system, and carrying four machine guns. After further work at Boulton Paul it would emerge as the Boulton Paul Type A turret, armed with four .303in Browning machine guns, and would be used in several aircraft including the Blackburn Roc and Handley Page Halifax.

The new turret greatly impressed the Air Ministry. Specification F.9/35 was written around the turret, and called for a day and night fighter. Boulton Paul were only one of five companies that responded to this specification. Designs from Armstrong Whitworth, Bristol and Supermarine were rejected at the first stage, leaving only Boulton Paul and Hawker in the contest. The Hawker Hotspur progressed as far as the unarmed prototype stage, but Hawker were now increasingly busy producing the Hurricane, and withdrew from the contest. This left the Boulton Paul Project 82, soon called the Defiant, as the only contender in the field.

Boulton Paul Defiant I front plan
Boulton Paul Defiant I front plan

The first Defiant prototype flew on 11 August 1937, without its turret. Superficially it resembled the Hurricane, especially in the lines of the rear fuselage, with the obvious exception of the Boulton Paul Type A Mk IID turret, just behind the pilot’s cockpit. The turret placement was well designed, causing relatively little drag. However, the weight of the turret meant that the Defiant was 1,500lbs heavier than the Hurricane, despite being powered by the same Rolls Royce Merlin engine. Even so, the prototype had a top speed of 302 mph. The Defiant was one of a number of aircraft (amongst then the Fairey Battle) ordered into production before the flight of the first prototype. In the case of the Defiant, the first order, for 87 aircraft, was placed on 28 April 1937.

Boulton Paul Defiant I front plan
Boulton Paul Defiant I top plan

Development was slow, partly because official tests on the turret took too long. The first production aircraft did not fly until 30 July 1939. Squadron deliveries began in December 1939, when No. 264 Squadron became the first to receive the new aircraft. Comparative tests against the Hurricane and Spitfire quickly revealed that the Defiant was comparatively slow and had limited manoeuvrability.

Despite this, the Defiant had a spectacular combat debut over Dunkirk. German fighter pilots were not expecting to encounter a turret armed fighter of this size. Encountering a formation of Defiants, the German fighters would attack from above and behind, the blind spot for most fighters, and run into a hail of bullets from the turret. On one day alone (29 May) the Defiants claimed 37 victories, although this would appear to be something of an overestimate.

The Germans did not take long to realise what was happening, and after that the Defiant’s days as a day fighter were numbered. It was highly vulnerable to attacks from below or from the front. On 31 May seven Defiants were lost, and No. 264 Squadron was soon transferred to convoy patrol duty. A second Defiant squadron, No. 141, remained operational from 1 July to 21 July before being withdrawn after suffering heavy losses.

Boulton Paul Defiant K8310
Boulton Paul Defiant

This was not the end of the Defiant's career. The RAF had very few aircraft capable of operating as night fighters. The Bristol Blenheim, while had quickly been pressed into that role, lacked the speed to catch German bombers, while the Bristol Beaufighter was only just coming into service at the end of 1940. However, there were a large number of Defiants coming off the production lines. The main problem faced by the Defiant as a night fighter over the crucial winter of 1940-1 was that the contemporary radar equipment was too bulky to fit into the aircraft, and so its first winter as a night fighter saw it achieve very little, although some confirmed kills were made.

During 1941 AI Mk IV and Mk IV appeared, both of which could fit in the Defiant. When equipped with radar, the Defiant was designated as the NF.Mk IA, and in this configuration became a relatively successful night fighter, equipping thirteen night fighter squadrons, seven retaining the type well in 1942.

The Defiant had a final lease of life with training units, both as a target tug and as a gunnery trainer, even serving with the Royal Navy. Production continued until 1943. The Defiant had been designed to fill a possible gap if the new generation of high speed forward firing fighter aircraft failed in combat. In the event the Supermarine Spitfire and Messerschmitt Bf 109 proved that the high speed, manoeuvrable fixed gun fighter was the superior design, but in 1935 such aircraft had yet to prove themselves in combat.


Mk I
Engine: Merlin II
Max Speed: 304 mph at 17,000 ft
Cruising Speed: 259mph at 15,000 ft
Ceiling: 30,350
Range: 465 miles
Span: 39 ft 4 in
Length: 35 ft 4in
Armament: Four .303in Browning machine guns in Boulton Paul Type A turret.

Boulton Paul Defiants of No.264 Squadron
Boulton Paul Defiants of No.264 Squadron

Engine: Merlin XX
Horsepower: 1,280 hp
Maximum Speed: 313 mph at 19,000 ft
Cruising Speed: 260 mph at 20,000 ft
Ceiling: 30,350ft
Range: 515 miles
Span: 39 ft 4 in
Length: 35ft 8 in
Armament: Four .303in Browning machine guns in Boulton Paul Type A turret.

Production Figures
Mk I: 705
Mk II: 220
TT. Mk I: 140
Total: 1,065

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How to cite this article: Rickard, J (19 April 2007), Boulton Paul Defiant,

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