Boulton Paul Defiant

The Boulton Paul Defiant is a British interceptor aircraft that served with the Royal Air Force (RAF) during World War II. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter" to meet the RAF requirement for day and night fighters that could concentrate their firepower on enemy bombers which were not expected to have fighter escorts due to the distance from Germany to the United Kingdom. The Defiant had all its armament in a dorsal turret offering the ability to fire in most directions. The same principle was used in the Royal Navy's Blackburn Roc which was also built by Boulton Paul.

In combat, the Defiant was found to be effective at destroying unescorted bombers, the role it was designed for, but was vulnerable to the Luftwaffes more manoeuvrable, single-seat Messerschmitt Bf 109 fighters operating from bases in Northern France, allowing them to escort bombers to London, although with fuel for only ten minutes of flying time there. The Defiant had been designed only to destroy unescorted bombers by means of beam or ventral attacks, and had no forward-firing armament; it proved to be very vulnerable to frontal attacks by fighters in daylight combat. It was withdrawn from daytime operations for use as a night fighter, and found success in combination with the use of aircraft interception radar (A.I.) to locate the enemy. It eventually equipped thirteen squadrons in this role, compared to just two squadrons as a day-fighter, though this was mainly due to slow initial production. In mid-1942 it was replaced by better-performing night fighters, the Bristol Beaufighter and de Havilland Mosquito.

Development

Origins

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 penetrate British airspace with impunity. The RAF did not expect bombers to be escorted by fighters because fighters would not have the range to reach the UK from Germany. 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 increasingly inadequate to effectively respond to ever-faster hostile aircraft, thus there was considerable interest in using a power-augmented turret. 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, the concept and development work of which would later be a core part of the Defiant design. In September 1935 the Air Ministry picked Hawker, Boulton Paul and Armstrong Whitworth designs as the top three (in decreasing order); Gloster and Bristol were rejected due to their turret designs. The Air Ministry wanted several designs investigated and the production of two prototypes of each. To get this large number of aircraft, HM Treasury had to approve the expenditure above that already allocated.

P.82

Boulton Paul, having been focused on turret-equipped aircraft for some time, made a submission to Specification F.9/35 with the company designation of P.82. The 'Type A' turret was an electro-hydraulically powered "drop-in" unit, with crank-operated mechanical backup. Small bombs could be housed in recesses in the outer wing. 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 and subsequently was declared the victor of the turret fighter competition. 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. Later versions of the AI radar were adopted over time, such as the AI Mk VI. The need for both the Defiant (and the Hurricane) in the night fighter role petered out by 1942 as the larger Bristol Beaufighter became the RAF's primary night fighter type, freeing both aircraft for other duties.

The last Defiant Mk IIs under construction were completed as TT Mk I aircraft. Dozens of existing Defiant Mk Is would be remanufactured to the similar Defiant TT Mk III standard; roughly 150 of such conversions took place during 1943–1944. Ultimately, the only use of the Defiant within the FAA was its adoption of the target tug version. It was a relatively clean design and made use of a simple, weight-saving structure.). Some versions (P.82) could carry a few small bombs. The fuselage was fitted with aerodynamic fairings that helped mitigate the drag of the turret; they were pneumatically powered and automatically raised and 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. as were several contemporaneous designs arising from Air Ministry specifications.

thumb|upright|An air-gunner of 264 Squadron wearing a 'GQ Parasuit', or "rhino suit", August 1940

Limitations of the armament were inability of the guns to fire directly forwards in normal operation (the guns could not fire within 16 degrees of the line of flight), and the guns' inability to fire downwards, so the aircraft had to remain below the enemy. This was suitable for attacking bombers from below, but not for dogfighting with fighters. As flying and the guns were operated by different people, there was a need to communicate; the gunner was distracted from his firing by having to direct the pilot over the intercom.

The zero deflection gunnery technique was practised, among others, by British ace Albert Ball using Lewis guns on Foster mounts – which largely eliminated the need for either complex gun sights or aiming-off by eye. An elevation of +19° combined with ballistic properties of .303 Brownings and the Defiant's operational speed made 'line of sight' aiming – as practised by Luftwaffe pilots – a practical proposition. This technique, applied later in the war by Germany as Schräge Musik, seems to have been neither taught nor 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 F.9/37 (Gloster G9) twin-engine bomber-interceptor – armed with 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 operated the turret through a control column with the firing button on the top. The motor could be put in high speed mode for swift changes of direction and the there was a handle for manual rotation of the turret.

The gunner's hatch was in the rear of the turret, which had to be rotated to the 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; the parachute was stowed alongside the gunner instead. This made escape from the aircraft so difficult that gunners were later provided with a special all-in-one garment, a 'parasuit', 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".

Operational history

Air combat

thumb|Defiant Mk.I N1585, PS-A of No. 264 Sqn., [[RAF Kirton in Lindsey, July 1940]]

thumb|Defiant Mark I N3313 of [[No. 264 Squadron RAF|No. 264 Squadron, 1940]]

In October 1939, No. 264 (Madras Presidency) Squadron was reformed at RAF Sutton Bridge to operate the Defiant. Initial training, formal squadron acceptance, and development of tactics began with other aircraft as it received its first Defiants only in early December at Martlesham Heath. In February 1940, the Defiant commenced night fighter training operations; 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. It became clear during these trials that the Defiant was suited only to performing the unescorted bomber-destroyer duties it was designed for, and was vulnerable to fighters. On 12 May 1940, the first operational sortie occurred as a flight of six Defiants flew with six Spitfires of 66 Squadron over the English Channel to the coastline in the vicinity of The Hague, Netherlands; during this flight, a single Ju 88 which had been attacking a destroyer was shot down. The following day, in a patrol that was a repetition of the first, Defiants claimed four Junkers Ju 87 Stuka dive bombers, but were subsequently attacked by a flight of Bf 109Es. The escorting Spitfires were unable to prevent five of the six Defiants from 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.

thumb|left|upright|[[Flight Sergeants E R Thorn (pilot, left) and F J Barker (air gunner) pose with their Defiant after destroying their 13th Axis aircraft; Thorn and Barker were the most successful Defiant crew of the war.]]

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 could not bear and offered no defence. Defiant losses quickly mounted, particularly among the gunners, who were often unable to leave stricken aircraft. The additional weight and aerodynamic drag of the turret, and the weight of the gunner, gave the Defiant a lower performance than single-seat fighter aircraft.

264 Squadron 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 Squadron, 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 Squadron Defiants sent to cover a convoy off Folkestone were shot down by Bf 109s of JG 51, and the remaining two survived, one badly damaged, thanks only to the intervention of Hurricanes of 111 Sqn. The Hurricane pilots reported that the Defiants had shot down four Bf 109s. 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, leading to multiple claims.

On 22 August, in response to an urgent demand for aircraft to defend Britain's airspace, 264 Squadron relocated to RAF Hornchurch, Essex, while also using RAF Manston as a forward base. Three aircraft were lost, two to ace Hpt. Gunther Lutzow of JG 3, but six Do 17s and a Bf 109 were shot down.

The squadron lost a further five aircraft (to JG 26) on 28 August, with nine crew killed, and effectively ended operations, withdrawing to RAF Duxford the following day. It was concluded that when operating against escorted bombers the Defiant should always be sent into battle with a top cover of Hurricanes or Spitfires so it could concentrate on its designed role of shooting down the bombers, but this proved impractical, particularly as the Defiant's radio reception was relatively poor due to its underslung antenna. The decision was made to switch the type to night operations, and there the Defiant saw some success.

thumb|Groundcrew working on the Merlin engine of a Defiant at [[RAF Fairwood Common, Wales, January 1942]]

On 1 July, 141 Squadron despatched L6997 on the first Defiant night patrol. In August, the squadron was operating both by day and night; on 15 August, the first possible nighttime success by a Defiant was recorded, and from September onwards, the squadron principally operated at night. Successful claimed interceptions took place, such as two He 111s being claimed on 15/16 September; the first confirmed kill, of a single He 111, by a Defiant of the squadron was made on 22 December.

The Defiant night fighters had initially lacked aircraft interception radar; enemy aircraft were spotted by crew observation aided by ground-based searchlights illuminating attacking bombers.

The improved Defiant Mk II model was fitted with the AI Mk. IV radar and a Merlin XX engine, increasing the aircraft's performance, particularly at nighttime.

Other roles

thumb|A Defiant TT Mk I in flight

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 early 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.

thumb|left|Defiant TT Mk III target tug, number N1697; [[RAF Desford, May 1944. The wind-driven generator provided power for the target winch]]

In the air-sea rescue role, the Defiant was the intended replacement for the Westland Lysander in shallow air-sea rescue units. However, six months following their introduction to the role, the Defiant had proved to be a poor choice for the role, in part due to the aircraft already been worn out by their previous service, which limited the sortie rate; other issues included its high stalling speed and wide turning radius. There were further deployments 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: one to R Malcolm Ltd (later ML Aviation), and the other to Martin-Baker. Various trials using DR944 were made until May 1948. The other Defiant, AA292, was delivered to R Malcolm Ltd at White Waltham Airfield on 15 April 1945, and the first airborne trial with dummies was held that October.

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

Variants

thumb|A formation of Defiants

thumb|Several parked Defiants

;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 aircraft 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 aircraft interception radar; 210 built.

;Defiant TT Mk III

:Dedicated turret-less target tug; 140 built from new.

Operators

British India

Surviving aircraft

thumb|left|Defiant N1671, RAF Museum Cosford, 2023

The only surviving complete example of the type is a Defiant I, N1671, on display as a night fighter at the Royal Air Force Museum Cosford in Shropshire. It was one of four Defiants delivered to No. 307 Polish Night Fighter Squadron at RAF Kirton in Lindsey, Lincolnshire on 17 September 1940 It was returned to Hendon on 6 December 2012, and was then moved from Hendon to Royal Air Force Museum Cosford in November 2016 for display in the War in the Air hangar.

Major parts of at least two other Defiants survive; N1766 and N3378, both Mk Is. A full-scale replica Defiant was created on site at Boulton Paul in Wolverhampton by ex-Boulton Paul engineer Jack Holmes and team at the Boulton Paul Heritage Society. More than 50,000 man hours went into its production and it was unveiled in 2003 marking 60 years since the last Defiant flew out of Pendeford (the World War II training airfield next to the Boulton Paul Factory in Wolverhampton). Due to change of ownership at the Boulton Paul site, the Defiant faced losing its home in Wolverhampton, and in 2015 was relocated to its now permanent home on display at the Kent Battle of Britain Museum in the colours of 264 Squadron (L7005).

Specifications (Mk I)

thumb|Closeup view of the turret of a Defiant with its four [[.303 British|0.303 in (7.7 mm) Browning machine guns]]

Notes

References

Citations

Bibliography

Ansell, Mark. Boulton Paul Defiant. Redbourn, Herts, UK: Mushroom Model Publications, 2005. .
Bowyer, Michael J.F. "The Boulton Paul Defiant." Aircraft in Profile, Vol. 5. London: Profile Publications Ltd., 1966.
Brew, Alex. The Turret Fighters – Defiant and Roc. Ramsbury, Marlborough, Wiltshire, UK: Crowood Press, 2002. .
Brew, Alex. The Defiant File. Tonbridge, Kent, UK: Air-Britain (Historians) Ltd., 1996. .
Buttler, Tony. British Secret Projects: Fighters & Bombers 1935–1950. Hinckley, UK: Midland Publishing, 2004. .
Carter, Graham. ML Aviation Ltd: A Secret World. Chippenham: Keyham Books, 2006.
Caygill, Peter. Flying to the Limit: Testing WW II Single-engined Fighters. Casemate Publishers, 2005.
Green, William. War Planes of the Second World War: Fighters, Vol. 2. London: Macdonald & Co., 1961. No ISBN.
Green, William and Gordon Swanborough. WW2 Aircraft Fact Files: RAF Fighters, Part 1. London: Macdonald and Jane's Publishing Ltd., 1978. .
Hall, Alan W. and Andrew Thomas. Boulton Paul Defiant (Warpaint Series No. 42). Luton, Bedfordshire, UK: Warpaint Books, 2003.
Mondey, David. The Hamlyn Concise Guide to British Aircraft of World War II. London: Chancellor Press, 2002. .
Nijboer, Donald. Gunner: An Illustrated History of World War II Aircraft Turrets and Gun Positions. Shrewsbury, UK: Airlife Publishing Company Limited (reprinted by Boston Mills Press (Canada), 2001. .
Price, Alfred. Instruments of Darkness: The History of Electronic Warfare. St. Albans, UK: Granada, 1979. .
Taylor, John W.R. "Boulton Paul Defiant." Combat Aircraft of the World from 1909 to the present. New York: G.P. Putnam's Sons, 1969. .
.
Whitehouse, Les. "The Disappointing Defiant." Air Enthusiast Volume 5, November 1977 – February 1978. Bromley, Kent, UK: Pilot Press Ltd., 1977.
Wheeler, Barry C. The Hamlyn Guide to Military Aircraft Markings. London: Chancellor Press, 1992. .
Winchester, Jim. "Boulton Paul Defiant." The World's Worst Aircraft: From Pioneering Failures to Multimillion Dollar Disasters. London: Amber Books Ltd., 2005. .

External links

Aeroflight.co.uk
The Boulton Paul Association
"Boulton Paul Defiant." Flight, 12 February 1942, pp. 132–135.
in German featuring Boulton Paul P.94