Boulton Paul Defiant
|Boulton Paul Defiant Mk I|
|Role||Two-seat fighter, night fighter, trainer, target tug|
|Manufacturer||Boulton Paul Aircraft|
|Designer||John Dudley North|
|First flight||11 August 1937|
|Primary users||Royal Air Force
Royal Australian Air Force
Royal Canadian Air Force
Polish Air Force
The Boulton Paul Defiant was a British interceptor aircraft that served with the Royal Air Force (RAF) during the Second World War. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter", without any forward-firing guns. It was a contemporary of the Royal Navy's Blackburn Roc. The concept of a turret fighter related directly to the successful First World War-era Bristol F.2 Fighter.
In combat, the Defiant was found to be reasonably effective at its intended task of destroying bombers but was vulnerable to the Luftwaffe's more manoeuvrable, single-seat Messerschmitt Bf 109 fighters. The lack of forward-firing armament proved to be a great weakness in daylight combat and its potential was only realised when it was converted to night fighting. It was supplanted in the night fighter role by the Bristol Beaufighter and de Havilland Mosquito. The Defiant found use in gunnery training, target towing, electronic countermeasures and air-sea rescue. Among RAF pilots it had the nickname "Daffy".
During the 1930s, the increasing speed of military aircraft posed a particular challenge to anti-aircraft defences. Advances in aircraft design achieved during the 1920s and 1930s had resulted in a generation of multi-engined monoplane bombers that were substantially faster than their contemporary single-engined biplane fighters then in service. The RAF came to believe that its new generation of turret-armed bombers, such as the Vickers Wellington, would be capable of readily penetrating enemy airspace and of defending themselves without any accompanying fighter escort, but also recognised that the bombers of other European air forces, such as the Luftwaffe, would similarly be able to successfully penetrate British airspace with inpunity.
During 1935, the concept of a turret-armed defensive fighter to counter the bomber threat emerged during a time in which the RAF anticipated having to defend Great Britain against massed formations of unescorted enemy bombers. In theory, turret-armed fighters would approach an enemy bomber from below or from the side and coordinate their fire. The separation of the tasks of flying the aircraft and firing the guns, would allow the pilot to concentrate on putting the fighter into the best position for the gunner to engage the enemy. However, manually-traversed turrets were viewed as having becoming more problematic and increasingly inadequate to effectively respond to ever-faster hostile aircraft, thus there was considerable interest in using a power-augmented turret arrangement.
The earlier Hawker Demon biplane had tested the concept with 59 of the fighters, which had been manufactured by Boulton Paul under a sub-contract, having been equipped with a hydraulically-powered rear turret, while a number of aircraft already built were also converted as such. Boulton Paul and its managing director John Dudley North had gained considerable experience with defensive turrets from producing several earlier aircraft, including the Boulton Paul Overstrand bomber, and had devised a four-gun power-operated turret arrangement, the concept and development work of which would later be a core part of the Defiant design.
In April 1935, the Air Ministry released Specification F.9/35, which required a two-seater day and night "turret fighter" capable of 290 miles per hour (470 km/h) at 15,000 feet (4,600 m). The aircraft was to feature a clean design, concentrating its armament within a power-operated turret, and the accepted performance of which was to be only slightly beneath that of other emergent fighter designs of the period, along with a sufficient fuel capacity to allow it to perform standing patrols. In particular, the powered turret was to offer considerable flexibility, possessing both a 360-degree upper hemisphere field of fire and be able to engage enemy bombers from a range of quarters, specifically below the aircraft itself. Specification F.9/35 had followed the earlier Specification F.5/33, which had sought a pusher design combined with a forward-set turret; F.5/33 had been unceremoniously abandoned as the proposals had offered little in terms of performance gains over existing fighters and the corresponding Armstrong Whitworth AW.34 design which had been ordered was not completed.
Boulton Paul, having been focused on turret-equipped aircraft for sometime already, decided to make a submission in response to Specification F.9/35; their design was given the internal designation of P.82. The proposed fighter was broadly similar in both size and appearance to the more conventional Hawker Hunter, differing in weight primarily due to the former's use of turret-based armaments. The central feature of the P.82 was its four-gun turret, based on a design by French aviation company Societe d'Applications des Machines Motrices (SAMM), which had been licensed by Boulton Paul for use in the earlier Boulton Paul Sidestrand bomber but eventually installed in the "follow-up" design, the Boulton Paul Overstrand and Blackburn Roc naval fighter. The 'Type A' turret was an electro-hydraulically powered "drop-in" unit, outfitted with a crank-operated mechanical backup. In addition, small bombs could be housed in recesses within the outer wing. Some of the development work from the company's earlier B.1/35 tender was carried over into the P.82.
Of the seven designs tendered, the Air Ministry ranked the P.82 as being the second-best submission, after Hawker's Hotspur but ahead of others such as Armstrong Whitworth's twin-engined design. The Air Ministry wanted several designs investigated and the production of two prototypes of each, but the associated costs involved in this preference were in excess of the allocated funding thus special permission from HM Treasury was sought. The Treasury agreed to finance the completion of seven prototypes (two Hawker, two Boulton Paul, two Fairey and one Armstrong Whitworth); however, only prototypes of the two most promising designed, the P.82 and the Hotspur, were ultimately ordered in late 1935. In 1936, Boulton Paul commenced assembly on the first P.82 prototype, K8310, at their newly-established Wolverhampton facility; an order for a second prototype, K8620, was received by the following year.
In 1937, the first P.82 prototype, K8310, was rolled out. Furnished with a 1,030 hp (768 kW) Rolls-Royce Merlin I and initially lacking its turret, the aircraft bore a great resemblance to the contemporary Hawker Hurricane, although it was at least 1,500 pounds (680 kg) heavier. On 11 August 1937, K8310, which had recently received the name Defiant, conducted its maiden flight. This initial flight, piloted by Boulton Paul's chief test pilot Cecil Feather, occurred nearly a year ahead of the rival Hotspur, but it did not have a turret fitted at the time. Official acceptance trials did not commence until nine months later. On 30 July 1939, the second prototype, K8620, equipped with a Merlin II engine and a full turret, conducted its first flight. K8620 had received various modifications over the first prototype, such as the installation of telescopic radio masts along with revisions to the canopy and to the undercarriage fairing plates; implementing these improvements had incurred delays to the completion of the second prototype.
Production orders had been prepared for the Hotspur, the initial front-running submission; however, Boulton Paul's turret design had gained the attention of the Air Ministry. In addition, Hawker's progress on the project had been delayed by the heavy commitments on other aircraft programs that it was conducting at the time, one being the more conventional Hurricane; thus the prototype Hotspur, K8309, did not conduct its maiden flight until 14 June 1938. On 28 April 1937, an initial production order for 87 aircraft was received by Boulton Paul for the P.82; as this was prior to the first flight of the prototype, the aircraft had effectively been ordered 'off the drawing board'. The order for the rival Hotspur was cancelled in 1938.
Completing its acceptance tests with the turret installed, the Defiant attained a top speed of 302 miles per hour (486 km/h) and subsequently was declared the victor of the turret fighter competition. Flight trials had revealed the aircraft to possess positive flight characteristics and considerable stability, which was of particular value when using the turret. According to aviation author Michael Bowyers, the usefulness of the Defiant had suffered due to the overly long development time for the type, observing that the Defiant's service entry was delayed to such an extent that only three production aircraft had reached the RAF, and these were only for trial purposes, by the outbreak of the Second World War. Due to delays with the type entering production, there were not enough available Defiants to begun standing patrols in 1940, by which point the introduction of not only more advanced fighters but bombers as well had allegedly undermined the usefulness of the type.
On 30 July 1939, the first production Defiant, L6950, conducted its maiden flight; it commenced official trials with the Aeroplane and Armament Experimental Establishment (A&AEE) in September that year. Apart from some detail changes, the production Defiant Mk I looked similar to the two Defiant prototypes. It was powered by the Rolls Royce Merlin III engine, which was capable of generating 1,030 hp/768 kW or 1,160 hp/865 kW of thrust.[N 1]
By January 1940, over half of the original production batch had been completed. Beyond the initial production order in April 1937, follow-on orders had been issued for the type; in February 1938, an additional 202 Defiant Mk I aircraft were ordered; three months later, another 161 aircraft were ordered. In December 1939, yet another 150 aircraft were ordered, raising the overall total to 513. In 1940, this rose to 563 Defiant Mk Is on order, while a further 280 were ordered under a rearranged manufacturing plan issued in mid-1940. However, the performance of the Defiant had been determined to be inadequate by this point, which led to manufacturing being sustained principally for economic reasons. A total of 713 Defiant Mk I aircraft were completed.
In response to a service request which sought greater performance, the Defiant Mk II, powered by the 1,260 hp Merlin XX engine, was promptly developed. On 20 July 1940, N1550, the first production Defiant Mk II, performed its initial flight.
The P.85 was Boulton Paul's tender to Specification O.30/35 for the naval turret fighter. A version of the Defiant for Fleet Air Arm (FAA), it had a deeper fuselage and leading edge slats, for the lower landing speeds required of carrier aircraft. The engine would be either a Bristol Hercules radial or the Merlin. Despite a higher estimated top speed, the Blackburn Roc was selected. With Blackburn already busy producing other projects, the detail design and production of the Roc was given to Boulton Paul. The only FAA use of the Defiant was as the target tug version.
The first Defiant prototype had not been fitted with a turret at first and had an impressive top speed. In 1940, Boulton Paul removed the turret from the prototype as a demonstrator for a fixed-gun fighter based on Defiant components. The armament offered was either 12 .303 inches (7.7 mm) Browning machine guns (six per wing) or four 20 millimetres (0.79 in) Hispano cannon in place eight of the Brownings. The guns could be depressed for ground attack. By that time, the RAF had sufficient quantities of Hawker Hurricanes and Supermarine Spitfire and did not require a new single-seat fighter. With a calculated top speed of about 360 miles per hour (580 km/h) at 21,700 feet (6,600 m) the P.94 was almost as fast as a contemporary Spitfire although less manoeuvrable.
The Defiant is a single-engine interceptor aircraft. It used a monoplane structure which was coupled with main landing gear which retracted into a broad mainplane section. The pilot's cockpit and rear turret were faired into a streamlined upper fuselage section. Tankage for up to 104 gallons of fuel was housed within the wing centre section along with a large ventral radiator that completed the resemblance to the Hawker fighter. The center section employed a two-spar arrangement, the wing itself containing and possessing removable wingtips. The rear fuselage comprised two metal cones connected by a two-foot transitional section and a flat upper deck. The Defiant employed an all-metal stressed skin monocoque structure, which was built in sections that were subsequently bolted together, a manufacturing method previously used on other Bolton Paul-designed aircraft. It was a relatively clean design and made use of a simple, weight-saving structure.
The primary mission of the Defiant was the destruction of incoming enemy bombers. The principal armament of the aircraft is its powered dorsal turret, equipped with four 0.303 in (7.7 mm) Browning machine guns. The fuselage was fitted with aerodynamic fairings that helped mitigate the drag of the turret; they were pneumatically powered and could be lowered into the fuselage so that the turret could rotate freely. The Brownings were electrically fired and insulated cut-off points in the turret ring prevented the guns firing when they were pointing at the propeller disc or tailplane. The gunner could rotate the turret directly forward and transfer firing control of the guns to the pilot, with the guns firing along each side of the cockpit canopy; this was rarely done as the turret's minimum forward elevation was 19° and the pilot did not have a gunsight, possibly because the Defiant was outfitted to perform zero deflection shooting, as were several contemporaneous designs arising from Air Ministry specifications.
The zero deflection gunnery technique was practised, among others, by British ace Albert Ball using Lewis guns on Forster mounts - which largely eliminated the need for either complex gun sights or aiming-off by eye (Kentucky windage). An elevation of +19° combined with ballistic properties of .303 (7.7mm) Brownings and the Defiant's operational speed made 'line of sight' aiming - as practised by Luftwaffe pilots - a practical proposition. This technique (described more fully in the article Schräge Musik) seems neither to have been taught or practised by the RAF. Despite being common knowledge among veteran First World War aircrew, featuring in Air Ministry requirements reflected in fighter designs such as the contemporaneous Gloster G9 twin-engine bomber-interceptor - armed with no fewer than five 20mm cannon at +12° - virtually all losses of Bomber Command aircraft shot down by Luftwaffe night fighters using upward-firing were ascribed to flak until 1944.
The gunner's hatch was in the rear of the turret, which had to be rotated to a side for entry and exit. There was not enough room in the turret for the gunner to wear a seat-type or back pack parachute so gunners were provided with a special all-in-one garment nicknamed the "rhino suit". Frederick "Gus" Platts, an air gunner who served in 230, 282 and 208 squadrons, stated: "The Rhino suit we had to wear on Defiants was a bear but I couldn't come up with an alternative, even though it killed dozens of us. I forget the details of it but we could not have sat on our chute or even keep it nearby as in other turrets, so you wore – all in one – an inner layer that fitted a little like a wetsuit of today. The chute fitted around this, and then the dinghy and the outer clothing. There was inner webbing and pockets that literally fell apart (I presume) when one bailed out".
In October 1939, No. 264 (Madras Presidency) Squadron was reformed at RAF Sutton Bridge to operate the Defiant. Initial training and development of tactics began with other aircraft as it received its first Defiants only in early December at Martlesham Heath. They began night fighter training in February 1940. The squadron tested its tactics against British medium bombers – Hampdens and Blenheims – and 264's CO flew against Robert Stanford Tuck in a Spitfire, showing that the Defiant could defend itself by circling and keeping its speed up. By March, 264 Squadron had two flights operational with Defiants and No. 141 Squadron received its first Defiant. When the Defiant was first introduced to the public, the RAF put out a disinformation campaign, stating that the Defiant had 21 guns: four in the turret, fourteen in the wings and three cannon in the nose.
The first operational sortie came on 12 May 1940. Defiants flew with six Spitfires of 66 Sqn, and a Ju 88 was shot down over the Netherlands. The following day, in a patrol that was a repetition of the first, Defiants claimed four Ju 87s, but were subsequently attacked by Bf 109Es. The escorting Spitfires were unable to prevent five of the six Defiants being shot down by a frontal attack.
During the evacuation of the British Expeditionary Force from Dunkirk, the squadron was based at RAF Manston, as one of the 16 squadrons that No. 11 Group had for the evacuation. On 27 May, 264 Sqn claimed three He 111 and two damaged. On 28 May, shortly after take-off, ten Defiants were attacked by about 30 Bf 109s – forming a circle, they claimed six German fighters for the loss of three Defiants. The Defiant was initially successful against enemy aircraft and its best day was 29 May, when No. 264 Sqn claimed 37 kills in two sorties: 19 Junkers Ju 87 Stuka dive bombers, mostly picked off as they came out of their dives, nine Messerschmitt Bf 110 twin-engined heavy fighters, eight Bf 109s and a Ju-88. One Defiant gunner was lost after he bailed out, although the aircraft made it back to its base to be repaired.
Luftwaffe fighters suffered losses when "bouncing" flights of Defiants from the rear, apparently mistaking them for Hurricanes. The German pilots were unaware of the Defiant's rear-firing armament and encountered concentrated defensive fire. The Luftwaffe changed tactics, to outmanoeuvre the Defiant and attack from below or dead ahead, where the turret guns offered no defence. Defiant losses quickly mounted, particularly among the gunners, who were often unable to leave stricken aircraft. The additional weight of the turret and the second crewman plus the aerodynamic drag gave the Defiant a lower performance than conventional single-seat fighter aircraft.
No 264 Sqn. developed a counter against single-seat aircraft such as the Bf 109. By flying in an ever-descending Lufbery circle, Defiant crews sacrificed the advantage of height but eliminated the possibility of attack from underneath, while giving 360° of defensive fire. This tactic was used by 264 Sqn. but when the Defiants of 141 Sqn were committed to combat a few months later during the Battle of Britain, it chose to ignore their advice. On 19 July, seven out of nine 141 Sqn Defiants sent to cover a convoy off Folkestone, were shot down by Bf 109s of JG 51 and the remaining two only survived, one badly damaged, thanks to the intervention of Hurricanes of 111 Sqn. The Hurricane pilots reported that the Defiants had shot down four Bf 109s.[N 2] Although 264 Squadron claimed 48 kills in eight days over Dunkirk, the cost was high with 14 Defiants lost. Actual German losses were no more than 12–15 enemy aircraft; the turret's wide angle of fire meant that several Defiants could engage the same target at one time, leading to multiple claims.
On 26 August, 264 Squadron engaged a formation of 12 Dornier Do 17 bombers over north-eastern Kent but was attacked by a large formation of Bf 109s. Three aircraft were lost (two to ace Hpt. Gunther Lutzow of JG 3) but six Do 17s and a Bf 109 were shot down. Three of those victories were awarded to one Defiant, crewed by Flight Sergeants E. R. Thorn (pilot) and F. J. Barker (air gunner). They shot down two Do 17s but were then engaged by a Bf 109 which set their Defiant on fire; they managed to shoot down the German fighter before making a forced landing. For this, they were awarded a bar to the Distinguished Flying Medal.[N 3] The squadron lost a further five aircraft (to JG 26) on 28 August, with nine crew killed. With these losses, the Defiant—which had been intended from the start as a day and night fighter—was transferred to night operations and achieved some success.
Defiant night fighters typically attacked enemy bombers from below, in a similar manoeuvre to the later German Schräge Musik methods. Defiants attacked more often from slightly ahead or to one side, rather than from directly under the tail. During the winter Blitz on London of 1940–41, the Defiant equipped four squadrons, shooting down more enemy aircraft than any other type. The turret-fighter concept was not immediately discarded and the fitting of Defiant-type turrets to Beaufighter and Mosquito night fighters was tried to enable these aircraft to duplicate these methods but the deleterious effect on performance proved drastic and the idea was abandoned. The Defiant Mk II model was fitted with the AI Mk. IV Airborne Interception radar and a Merlin XX engine and 207 were built.
After trials in 1940 with the School of Army Co-operation to assess its capabilities in that role, the Defiant was tested as a high-speed gunnery trainer with the Air Ministry agreeing to continue production. The Defiant was removed from combat duties in 1942 and used for training, target towing, electronic countermeasures and air-sea rescue.
Two types of electronic countermeasures equipment were carried by the Defiant, both countering the German Freya early warning radar. The first system to be deployed was "Moonshine", which re-transmitted the radar's signals to simulate large formations of aircraft. As each "Moonshine" transmitter only covered part of the Freya's frequency, a formation of eight Defiants was needed, giving the appearance of over 100 aircraft. As the system required formation flying, it could only be used in daylight, where it could draw German fighters onto British fighters leaving another area relatively free for a British bombing raid. A "Special Duties Flight" was set up in May 1942 to use the new countermeasures equipment, with "Moonshine" being used for its first live test on 6 August 1942. Subsequently it was used operationally as part of "Circuses" against coastal targets and on 19 August in support of the Dieppe Raid. The Flight became No. 515 Squadron RAF on 1 October 1942, operations with "Moonshine" continuing until November 1942.
515 Squadron continued operations with the second countermeasures system, "Mandrel", a noise jammer which overwhelmed the signals from Freya. Individual Defiants were sent to orbit positions 50 miles (80 km) off the enemy coast. By using nine aircraft a 200-mile (320-km) gap could be made in the Germans' radar coverage. 515 Squadron flew its first mission using Mandrel on the night of 5/6 December 1942, continuing to use its Defiants for jamming operations until the spring of 1943, when it began to receive twin-engined Bristol Beaufighters which had longer range and could carry more electronic equipment. The Defiant flew its last jamming mission on 17 July 1943, with one aircraft being lost out of four sent out that night.
In the air-sea rescue role, the Defiant was equipped with a pair of underwing pods that contained dinghies. A further 140 Defiant Mk III aircraft were built; this model lacked the dorsal turret and was used as a target tug. Many of the surviving Mk I and Mk II Defiants also had their turrets removed.
In this final target towing variant, the Defiant ended up with a number of overseas assignments with both the RAF and Fleet Air Arm in the Middle East, Africa and India. Further deployments occurred to Canada, where the Defiant was used as a target tug and trainer with the British Commonwealth Air Training Plan.
Defiants were also used for "special" work including tactical evaluations with the RAF Gunnery Research Unit and the Air Fighting Development Unit (AFDU) at Farnborough. Two Defiants were issued for ejection seat development work; to R Malcolm Ltd and Martin-Baker. On 11 May 1945, Martin-Baker used Defiant DR944 to test their first ejection seat with dummy launches.
The last operational use of Defiants was in India, where they were used as target tugs.
- Defiant Mk I
- Two-seat turret fighter for the RAF, powered by a 1,030 hp (768 kW) Rolls-Royce Merlin III piston engine; 723 built.
- Defiant NF Mk I
- Defiant Mk I converted into night fighters
- Defiant NF Mk IA
- NF Mk I with Airborne Interception radar.
- Defiant ASR Mk I
- Mk I carrying air-dropped dinghies for air-sea rescue.
- Defiant TT Mk I
- Defiant Mk IIs converted to target tugs; 150 conversions.
- Defiant Mk II
- Two-seat night fighter for the RAF, powered by a 1,280 hp (954 kW) Rolls-Royce Merlin XX piston engine, and fitted with the AI Mk IV airborne interception radar; 210 built.
- Defiant TT Mk III
- Dedicated turret-less target tug; 140 built from new.
The single surviving complete example of the type is a Defiant I, N1671, on display as a night fighter at the Royal Air Force Museum in Hendon, London. It was one of four Defiants delivered to No. 307 Polish Night Fighter Squadron at RAF Kirton in Lindsey, Lincolnshire, England on 17 September 1940. It was passed to No. 153 Squadron at the end of October 41 and 285 Sqn in 1942. In 1954, it was identified for storage as a historical aircraft and passed to the RAF Museum in 1971.
Major parts of at least two other Defiants survive; N1766 and N3378, both Mk Is.
Specifications (Mk I)
- Crew: two: pilot, gunner
- Length: 35 ft 4 in (10.77 m)
- Wingspan: 39 ft 4 in (11.99 m)
- Height: 11 ft 4 in (3.46 m)
- Wing area: 250 ft² (23.2 m²)
- Empty weight: 6,078 lb (2,763 kg)
- Loaded weight: 8,318 lb (3,781 kg)
- Max. takeoff weight: 8,600 lb (3,909 kg)
- Powerplant: 1 × Rolls-Royce Merlin III liquid-cooled V12 engine, 1,030 hp (768 kW)
- Maximum speed: 304 mph (264 knots, 489 km/h) at 17,000 ft (5,180 m)
- Cruise speed: 175 mph (152 knots, 282 km/h) at 15,000 ft (4,570 m)
- Range: 465 mi (404 nmi, 749 km)
- Endurance: 1.78 hr
- Service ceiling: 31,000 ft (9,250 m)
- Wing loading: 33.27 lb/ft² (163.0 kg/m²)
- Power/mass: 0.124 hp/lb (204 W/kg)
- Climb to 15,000 ft (4,600 m): 8.5 min
- Aircraft of comparable role, configuration and era
- Related lists
- The normal rating used for Battle of Britain Hurricane Mk.Is, Spitfire Mk.Is and Defiants was 1,030 hp (768 kW); from June 1940 supplies of 100 octane fuel from America became available, increasing power.
- This action is sometimes called "slaughter of the innocents."
- One of the Dornier 17s shot down by 264 Squadron that day, 5K+AR of Kampfgeschwader 3, crash–landed on the Goodwin Sands; two crew died and two survived to become prisoners. The aircraft later became submerged under shallow water and is the only known intact surviving Dornier 17. On 10 June 2013, it was the subject of a recovery operation by the Royal Air Force Museum. The identify of the Defiant that shot it down is unknown.
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