Boulton Paul Defiant

The Boulton Paul Defiant was a British interceptor aircraft that served with the Royal Air Force (RAF) early in 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 practice, the Defiant was found to be vulnerable to the Luftwaffe's more agile, single-seat Messerschmitt Bf 109 fighters. It became used as a night fighter until it was supplanted in that role by the Bristol Beaufighter and de Havilland Mosquito. The Defiant found use in gunnery training, target towing, electronic countermeasures (ECM) and air-sea rescue. Among RAF pilots, it had the nickname 'Daffy', probably a diminutive of the word 'Defiant'.

Design and development

Evolution

The concept of a turret-armed defensive fighter emerged in 1935, at a time when the RAF anticipated having to defend Great Britain against massed formations^[1] of unescorted enemy bombers.^[2] Advances in aircraft design during the 1920s and 1930s had resulted in a generation of multi-engined bombers that were faster than the single-engined biplane fighters in service. The RAF believed that its turret-armed bombers, such as the Boulton Paul Defiant, would be able to penetrate enemy airspace and defend themselves without fighter escort and also that the German Luftwaffe would be able to do the same.

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 while the gunner could engage the enemy. Previously the Hawker Demon had tested the concept with 59 of the biplane fighters (manufactured by Boulton Paul under a sub-contract) equipped with a powered rear turret while the remainder of the series already manufactured were converted.^[3]

Air Ministry Specification F.9/35 required a two-seater day and night 'turret fighter' capable of 290 mph at 15,000 ft. It followed the earlier F.5/33 which was for a pusher design with a front turret. F.5/33 had been abandoned as it offered little over existing fighters and the Armstrong Whitworth AW.34 design which had been ordered was not completed.^[1]

P.82

Boulton Paul, who had considerable experience with turrets from their earlier Overstrand bomber, submitted their P.82 design. Of the seven designs tendered, the P.82 was ranked second after Hawkers but ahead of Armstrong Whitworths twin-engined design. The Air Ministry wanted several designs investigated and two prototypes of each. The Treasury agreed to seven prototypes (2 Hawker, 2 Boulton Paul, 2 Fairey and 1 Armstrong Whitworth).^[4] In the event only prototypes of the P.82 and Hawker were built. Production orders were prepared for the Hawker but the Boulton Paul turret had the Air Ministry's attention. Delays by Hawker who were more focussed on the Hurricane led to the P.82 receiving a production order in 1937 and the Hotspur order was cancelled in 1938.

The P.82 was a monocoque design constructed by bolting the sections together. This was the same as BP had used on other aircraft. The design had room for small bombs in recesses in the outer wing. Some of the development work from their B.1/35 tender carried over into the P.82

The central feature of the P.82 was the four-gun turret based on a design by French aviation company 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.^[5] The turret, 'Type A' was an electro-hydraulically powered 'drop-in' unit with a crank-operated mechanical backup. The Defiant was armed with a 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. However, in practice this was rarely done as the turret's minimum forward elevation was 19° and the pilot did not have a gunsight.

The gunner's hatch was in the rear of the turret, which had to be rotated to a side to enable 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'. To quote Frederick 'Gus' Platts, air gunner in 230, 282 and 208 squadrons, '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'.^[6]

The first P.82 prototype (K8310) was rolled out in 1937 without its turret, looking like the Hawker Hurricane, although it was at least 1,500 lb (680 kg) heavier. A clean, simple and compact monoplane structure had been achieved with main landing gear retracting into a broad mainplane section. The pilot's cockpit and rear turret were faired into a streamlined upper fuselage section. Fuel was carried in the wing centre section along with a large ventral radiator that completed the resemblance to the Hawker fighter. With a 1,030 hp (768 kW) Rolls-Royce Merlin I, the newly named 'Defiant' prototype first flew on 11 August 1937, nearly a year ahead of the Hotspur. A second prototype, K8620 equipped with a turret was modified with telescopic radio masts, revision to the canopy and changes to the undercarriage fairing plates.

Completing its acceptance tests with the turret installed, the Defiant reached a top speed of 302 mph (486 km/h) and subsequently was declared the victor of the turret fighter competition. Apart from detail changes, the production Defiant Mk I looked similar to the two Defiant prototypes. As Boulton Paul were busy producing the Blackburn Roc naval turret fighter, the Defiant's service entry was delayed to such an extent that only three aircraft had reached the RAF by the start of the war. The Mk I was powered by the Rolls Royce Merlin III (1,030 hp/768 kW or 1,160 hp/865 kW)^{[N 1]} with a total of 713 aircraft built.

P.85

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 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.^[7] The only FAA use of the Defiant was as the target tug version.

P.94

The first Defiant prototype had not been initially fitted with a turret and therefore 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 in (7.7 mm) Browning machine guns (six per wing) or 4 20mm Hispano replacing 8 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 mph (579 km/h) at 21,700 ft, the P.94 was almost as fast as a contemporary Spitfire although less manoeuvrable.

Operational history

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 only received their first Defiants in early December at Martlesham Heath.^[8] They began night fighter training in February 1940. The squadron tested their tactics against British medium bombers – Hampdens and Blenheims – and 264's CO flew against Robert Stanford Tuck in a Spitfire showing 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—i.e. four in the turret, fourteen in the wings and three cannons in the nose.^[9]

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 Holland. 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 forward based at RAF Manston one of the 16 Squadrons that No. 11 Group had available to cover the evacuation. On the 27th 264 Sqn claimed 3 He 111 and 2 damaged. On the 28th, shortly after take-off ten Defiants were attacked by about 30 Bf 109s – forming a circle, six German fighters were claimed for the loss of three Defiants.

The Defiant was initially successful against enemy aircraft. Its best day was 29 May 1940, 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 though the aircraft made base to be repaired.

Initially, Luftwaffe fighters suffered losses when 'bouncing' flights of Defiants from the rear, apparently mistaking them for Hurricanes.^[10] The German pilots were unaware of the Defiant's rear-firing armament and encountered concentrated defensive fire. With a change in Luftwaffe tactics, opposing fighters were able to out-manoeuvre the Defiant and attack it from below or dead ahead, where the turret 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 lower performance than conventional fighter aircraft.^[11] According to the book The Turret Fighters by aviation historian Alec Brew, 264 Sqn. developed a counter against single-seat aircraft such as the Bf 109. By flying in an ever-descending Lufberry circle, Defiant crews sacrificed the advantage of height but eliminated the possibility of attack from underneath, while giving 360° of defensive fire.^[12] This tactic was used successfully 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 with devastating consequences. On 19 July 1940, seven out of nine Defiants of 141 Sqn. 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, due to the intervention of Hurricanes of 111 Sqn. The Hurricanes reported that the Defiants had shot down four Bf 109s.^{[13][N 2]} Although 264 Sqn. claimed 48 kills in eight days over Dunkirk, the cost was high with 14 Defiants lost. The actual German losses were no more than 12 to 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. 264 Squadron lost three aircraft on 26 August (two to ace Hpt. Gunther Lutzow of JG 3) and five on 28 August (to JG 26), with the deaths of nine crew members. With these losses, the Defiant - which had been intended from the start as a day and night fighter - was transferred to night fighting and there the Defiant achieved some success.

Defiant night fighters typically attacked enemy bombers from below, in a similar manoeuvre to the later successful 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.^[15] 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 effect on performance proved drastic and the idea was abandoned.^[16] The Defiant Mk II model was fitted with the AI Mk IV airborne interception radar and a Merlin XX engine. A total of 207 Mk II Defiants 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 were 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.^[17][18] 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.^[19] The Flight became No. 515 Squadron RAF on 1 October 1942, operations with 'Moonshine' continuing until November 1942.^[20]

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.^[21] 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.^[22]

In air-sea rescue the Defiant was equipped with a pair of under-wing 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.^[5] Further deployments occurred to Canada, where the Defiant was used as both 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.^[5]

The last operational use of Defiants was in India, where they were used as target tugs.^[23]

Variants

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 dingies 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.

Operators

Australia British India Canada Poland United Kingdom USA

Survivors

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.^[5][24] 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.^[25] 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. The aircraft was moved on 20 May 2009 to Rochester airport where it will be restored by the Medway Aircraft Preservation Society (MAPS).^[26] Major parts of at least two other Defiants survive; N1766 and N3378, both Mk Is.^[25]

Specifications (Mk I)

Data from War Planes of the Second World War: Volume Two Fighters^[27]

General characteristics

Crew: 2: 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)

Performance

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^[28] (9,250 m)
Wing loading: 33.27 lb/ft²^[8]
Power/mass: 0.124 hp/lb (204 W/kg) Climb to 15,000 ft (4,600 m): 8.5 min^[28]

Armament

Guns: 4 × 0.303 in (7.7 mm) Browning machine guns in hydraulically-powered dorsal turret (600 rpg)