Boulton Paul Defiant
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The Boulton Paul Defiant was an early World War II fighter aircraft of the Royal Air Force built by Boulton Paul Aircraft Ltd.
The design of the aircraft was an attempt to overcome the need to point the nose of a fighter at its target in order to bring the guns to bear. Instead of forward-facing guns, the Defiant was fitted with a powered dorsal turret equipped with four 0.303 in (7.7 mm) Browning machine guns. In theory, the Defiant would approach an enemy bomber from below and destroy it with a concentrated burst of fire. The concept was similar to the successful World War I Bristol Fighter but in practice the Defiant was cannon fodder for the more agile Luftwaffe Bf 109s. It was later used in the night fighter role where it had considerable success against less agile bombers, before it was phased out of combat operations.
Development
The idea of a fighter that carried its armament in a turret had cogent arguments and the Defiant was designed to Air Ministry Specification F.9/35 which required a powered turret as the sole armament. The Boulton Paul design was selected ahead of the Hotspur submitted by Hawker Aviation. While the Defiant prototype first flew on August 11, 1937 and immediately went into production as the Defiant Mk.I, its entry into service was delayed such 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 and a total of 713 were built.In practice the turret-only-armed fighter idea would be shown to be flawed. The additional weight of the turret (and second crewman) and the aerodynamic drag gave the Defiant much poorer performance than conventional fighter aircraft, and opposing fighters were able to out-maneouvre it and attack it from below where the turret offered no defence. The pilot had to guess where the guns were pointed, and the gunner could not anticipate violent manoeuvres by the pilot. The Defiant was limited also in that although the turret could turn a full circle, the interrupter gear which prevented the gunner from firing at any part of the aircraft also prevented him from firing forward through the propellor disc. The aircraft's performance problems were known early on, but the requirement for any fighters to supplement the Hurricances and Spitfires meant production proceeded.
According to the recent book The Turret Fighters by the renowned aviation historian Alec Brew, 264 Sqn developed effective countermeasures against single seat aircraft such as the Bf109. By flying in an ever-descending 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 successfully against Bf109's in action, but 141 Sqn chose to ignore their advice with devastating consequences.
Even the advantage of the turret fighter in the night fighter role was reduced with radar equipped airplanes which could locate and attack with their normal forward firing armament.
Combat history
No. 264 Squadron was the first to be equipped with the Defiant Mk.I in December 1939. The first operational sortie came on May 12, 1940. On May 13, a flight of six Defiants were attacked by Bf 109Es; five of the Defiants were shot down from a frontal attack.In late May during the evacuation of the BEF from Dunkirk, the Defiant had some success. Being visually similar to the Hawker Hurricane, it was initially able to surprise fighters attacking from the rear, but by the Battle of Britain a few months later its weaknesses were known and exploited. On July 19 six out of nine Defiants of No. 141 Squadron were shot down and the remaining three only survived due to the intervention of Hurricanes of No. 111 Squadron.
The Defiant was moved to night fighting duties and as a night fighter the Defiant achieved some success. 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. During the winter Blitz on London of 1940-41, the Defiant equipped four Squadrons.
The Defiant was removed from combat duties in 1942 and thereafter used for air/sea rescue, training and target towing. 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 May 1945, Martin-Baker used a Defiant to test their first ejection seat.
Boulton Paul also built the Blackburn Roc (from a design by Blackburn) which was the naval equivalent of the Defiant.
A surviving Defiant nightfighter is at the Royal Air Force museum in Hendon, London.
Specifications (Mk.I)
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