Often maligned as a failure, the Boulton Paul Defiant found a successful niche as a night-fighter during the German 'Blitz' on London, scoring a significant number of combat kills before being relegated to training and support roles.
The Boulton Paul company first became interested in powered gun turrets when it pioneered the use of a pneumatic-powered enclosed nose turret in the Boulton Paul Overstand biplane bomber. The company subsequently brought the rights to a French-designed electro-hydraulic powered turret and soon became the UK leaders in turret design.
On 26 June 1935, the Air Ministry issued Specification F.9/35 calling for a two-seat fighter with all its armament concentrated in a turret. Peformance was to be similar to that of the single-seat monoplane fighters then being developed. It was envisioned that the new fighter would be employed as destroyer of unescorted enemy bomber formations. Protected from the slipstream, the turret gunner would be able to bring much greater firepower to bear on rapidly moving targets than was previously possible.
The first prototype (K8310) made its maiden flight on 11 August 1937, with the turret position faired over as the first turret wasn't ready for installation. Without the drag of the turret, the aircraft was found to handle extremely well in the air. With these promising results, a further production contract was awarded in Febrary 1938. Performance with the turret fitted was somewhat disappointing, but still considered worthwhile. In May 1938, the second prototype (K8620)was ready for testing. This aircraft was much closer to the final production standard. Development and testing of the aircraft and turret combination proved somewhat protracted, and delivery to the Royal Air Force was delayed until December 1939, when No.264 Squadron received its first aircraft. Numerous engine and hydraulic problems were not finally resolved until early in 1940.
The Defiant undertook it first operational sortie on 12 May 1940, when 264 Sqn flew a patrol over the beaches of Dunkirk. A Junkers Ju 88 was claimed by the squadron. However, the unit suffered its first losses the following day, when five out of six aircraft were shot down by Bf 109s in a large dogfight. The Defiant was never designed to dogfight with single-seat fighters and losses soon mounted. By the end of May 1940, it had become very clear that the Defiant was no match for the Bf 109 and the two squadrons were moved to airfields away from the south coast of England. At the same time, interception of unescorted German bombers often proved successful, with several kills being made.
The limitations on the Defiant's manoeuvrability forced its eventual withdrawal from daylight operations in late August 1940. 264 and 141 squadrons became dedicated night-fighter units. The Defiant night fighters were painted all-black and fitted with flame damper exhausts. Success came quickly, with the first night kill being claimed on 15 September 1940. From November 1940, an increasing number of new night fighter squadrons were formed on the Defiant. Units operating the Defiant shot down more enemy aircraft than any other night-fighter during the German 'Blitz' on London in the winter of 1940-41.
The lack of forward firing armament presented a great handicap to a fighter which lacked the manoeuvrability to match single-seat fighters in combat, but as an interim night-fighter the Defiant met with a great deal of success.
Specifications (Mk I)
Crew: 2: pilot, gunner
Length: 35 ft 4 in (10.77 m)
Wingspan: 39 ft 4 in (11.99 m)
Height: 12 ft 2 in (3.71 m)
Wing area: 250 ft² (23 m²)
Empty weight: 6,078 lb (2,755 kg)
Loaded weight: 8,318 lb (3,773 kg)
Powerplant: 1× Rolls-Royce Merlin III liquid-cooled V12 engine, 1,030 hp (780 kW)
Maximum speed: 304 mph (264 knots, 489 km/h)
Range: 465 mi (404 nm, 748 km)
Service ceiling 30,350 ft (9,250 m)
Rate of climb: 1,900 ft/min (9.65 m/s)
Power/mass: 0.124 hp/lb (204 W/kg)
Guns: 4 × 0.303 in (7.7 mm) Browning machine guns in hydraulically-powered dorsal turret (600 rounds per gun, 2,400 rounds total)