Boulton Paul "Defiant" Mk.I
Boulton Paul "Defiant" Mk.I (N1671) at the Royal Air Force Museum London, Hendon Aerodrome, London, England (Photos by John Shupek)
Design and Development
The "Defiant" emerged at a time when the RAF anticipated having to defend Great Britain against unescorted enemy bombers. Advances in aircraft design during the 1920s and 1930s resulted in a generation of multi-engined bombers that were faster than the single-engined biplane fighters then in service. The RAF believed that its own turret-armed bombers, such as the Vickers "Wellington," would be able to penetrate enemy airspace and defend itself without fighter escort and that the German Luftwaffe would do the same. A turret-armed fighter would be able to engage enemy bombers from angles that would defeat the bomber gunners. Thus, the "Defiant" was armed 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 or beside and destroy it with a concentrated burst of fire.
Designed to meet the Air Ministry Specification F.9/35, which specified a "turret fighter" with a powered turret as the sole armament. Boulton Paul, who had considerable experience with turrets from their earlier "Overstrand" bomber, submitted their P.82 project. This design was selected as the most promising of seven initial proposals and one of only two prototypes constructed. The other competing design was the Hotspur from Hawker Aircraft.
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. The turret, the Type A, was an electro-hydraulically powered "drop-in" unit with a crank-operated mechanical backup. The fuselage was fitted with aerodynamic fairings that helped alleviate the drag of the turret; they were pneumatically powered and could be lowered into the fuselage so that the turret could rotate freely. The Browning guns were electrically fired, and insulated cut-off points in the turret ring prevented the guns from being activated when they were pointing at the propeller disc or tailplane.
The gunner entered and exited via a hatch in the rear of the turret, although there was a smaller exit in the lower fuselage that was more often used to load ammunition. As a consequence of this arrangement the gunner could not exit the "Defiant" quickly if the turret was rotated to point to the rear. There was not enough space in the turret for the gunner to wear a parachute, which was instead stowed in the Defiant's fuselage. In case of emergency, the gunner could transfer firing control of the guns to the pilot. In practice this was rarely done as the turret's minimum forward elevation was 19° and the pilot did not have a gunsight.
The first P.82 prototype (K8310) was rolled out in 1937 without its turret, looking superficially 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 center 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 installed, 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. However, its 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) with a total of 713 aircraft built.
P.85 The P.85 was a version of the "Defiant" for Fleet Air Arm (FAA) use, but the Blackburn "Roc" was selected and the only FAA use was to be the target tug version of the "Defiant."
P.94 The first "Defiant" prototype had not been initially fitted with a turret, and therefore had an impressive top speed. Consequently, in 1940, Boulton Paul developed a conventional, single-seat, turret-less version of the "Defiant" called the P.94, armed with 12 .303 in (7.7 mm) Browning machine guns (six per wing). By that time, the RAF had sufficient quantities of Hawker "Hurricanes" and Supermarine "Spitfires" and did not require a new single-seat fighter. With a top speed of about 360 mph (579 km/h), the P.94 was almost as fast as a contemporary "Spitfire," although less maneuverable.
Boulton Paul "Defiant" Mk.I
In December 1939, No. 264 Squadron at RAF Manston was the first to be equipped with the "Defiant" Mk I. The first operational sortie came on 12 May 1940 during the evacuation of the British Expeditionary Force from Dunkirk. The "Defiant" was initially successful against enemy aircraft. Its high-water mark was on 29 May 1940, when No. 264 Squadron claimed 65 kills, mostly Junkers Ju.87 "Stukas" and Messerschmitt Bf.110 twin-engined heavy fighters. Initially, Luftwaffe fighters suffered losses when "bouncing" flights of "Defiants" from the rear, apparently mistaking them for "Hurricane" fighters. The German pilots were unaware of the "Defiant's" rear-firing armament and encountered concentrated defensive fire. However, with a change in Luftwaffe tactics, opposing fighters were able to out-maneuver 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. On 13 May, a flight of six "Defiants" was attacked by Bf.109Es; five of the "Defiants" were shot down from a frontal attack.
According to the book The Turret Fighters by aviation historian Alec Brew, 264 Squadron developed effective countermeasures 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. This tactic was used successfully by 264 Squadron but when the "Defiants" of 141 Squadron were committed to combat a few months later during the Battle of Britain, 141 Squadron chose to ignore their advice, with devastating consequences. On 19 July 1940, six out of nine "Defiants" of 141 Squadron were shot down and the remaining three only survived due to the intervention of "Hurricanes" of 111 Squadron. Although 264 Squadron claimed an astonishing 48 kills in eight days over Dunkirk (recent research suggests no more than 12 to 15 enemy aircraft were actually destroyed; the turret's wide angle of fire meant that several "Defiants" could engage the same target at one time), the cost was high at 14 "Defiants" lost.
264 Squadron lost two aircraft on 26 August, then another five on 28 August with the deaths of nine crew members. With these prevailing losses, the "Defiant" was quickly transferred from daylight operations to night fighting duties and, as a night fighter, the "Defiant" achieved some success. "Defiant" night fighters typically attacked enemy bombers from below, in a similar maneuver 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. The turret-fighter concept was not immediately discarded and the fitting of Defiant-style turrets to "Beaufighter" and "Mosquito" night fighters was trialled to enable these aircraft to duplicate these methods, but the effect on performance proved drastic, and the idea was abandoned. 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 re-evaluated as a high-speed gunnery trainer, with the Air Ministry agreeing to keep the production lines open. The "Defiant" was removed from combat duties in 1942 and, thereafter, used for training, target towing, ECM and air sea rescue. The "Defiant" was used to carry the Mandrel noise jammer to combat the German "Freya" early warning radar. In the air-sea rescue role, 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. Further deployments occurred to Canada where the "Defiant" fulfilled a role as both a target tug and trainer with the British Commonwealth Air Training Plan.
Defiants were also utilized for "special" work including tactical evaluations with the RAF Gunnery Research Unit and Air Fighter Development Unit (AFDU) at Farnborough. On 11 May 1945, Martin-Baker used a "Defiant" (DR944), to test their first ejection seat with dummy launches.
The last operational use of "Defiants" was in India, where they were used as target tugs.
List of Boulton Paul "Defiant" operators:
Specifications — "Defiant" Mk.I