page_title: Boulton Paul Defiant
section_title: Origins
hierarchical_section_title: Boulton Paul Defiant / Development / Origins
caption_attribution_description: Royal Air Force Boulton Paul Defiant Mk Is of No. 264 Squadron RAF (including L7026 "PS-V" and N1535 "PS-A") based at Kirton-in-Lindsey, Lincolnshire, August 1940.
context_page_description: The Boulton Paul Defiant is a British interceptor aircraft that served with the Royal Air Force during World War II. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter", without any forward-firing guns, also found in the Blackburn Roc of the Royal Navy.
  In combat, the Defiant was found to be reasonably effective at 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 realised only when it was converted to night fighting. It was supplanted as a night fighter 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".
context_section_description: 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.
  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.
  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, 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 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 the ability to engage enemy bombers from a range of quarters, including 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.
caption: Defiants of No. 264 Squadron. The Squadron Leader's aircraft signified by the "A" on the fuselage
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