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Boulton Paul Defiant

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Designed as a bomber destroyer expected to engage unescorted aircraft, the Defiant was pressed into service as a day fighter and saw action over the beaches of Dunkirk and during the Battle of Britain. Despite early success, increasing losses saw the aircraft moved to night fighting during the winter of 1940. The Boulton Paul Defiant would go on to become the world's first electronic countermeasures aircraft.

Quick Facts
Boulton Paul Defiant side profile image
First flight
11th August 1937
Entered service
8th December 1939
Total built

Front view
Defiant front view photo
Side view
Defiant side view photo
Rear view
Defiant rear view photo

In the 1920s and 1930s it was proposed that fighters would have a gun turret mounted on them as opposed to forward firing guns as it was anticipated that enemy bombers attacking the UK would be unescorted. This appeared to have two advantages, firstly, it meant the pilot could concentrate on flying the aircraft and not have to worry about finding and hitting a target. Secondly the guns could be used over a greater area than before and could be used for both offence and defence.

When the Air Ministry issued Specification F.9/35 on the 26th June 1935 for a two-seater monoplane aircraft with a power operated gun turret that would be able to operate both at day and night, Hawker, Fairey, Supermarine, Gloster, Armstrong Whitworth and Boulton Paul all made submissions. Hawker's prototype, called the Hotspur, along with the Boulton Paul F.82 saw an order for two prototypes of each placed during October 1935. This was followed by an order for 87 of Boulton Paul's aircraft and 389 of the Hawker Hotspur on the 28th April 1937. However the only Hotspur prototype produced would not fly until the 14th June 1938, ten months after Boulton Paul's. By this time Hawker were committed to producing their Hawker Hurricane fighter and so development of the Hotspur was cancelled.

A two-seater, its crew consisting of a pilot and gunner, low-wing cantilever monoplane fighter of all metal construction with retractable tail wheel type landing gear and powered by a Rolls-Royce Merlin I engine the first prototype of Boulton Paul's aircraft, now called the Defiant, made its initial flight on the 11th August 1937 in the hands of Cecil Feathers, Boulton Paul test pilot, and minus its rear turret, which would be fitted during February 1938. On the 7th December 1937 the Defiant prototype was sent to the Aeroplane and Armament Experimental Establishment at Martlesham Heath for trials.

The second prototype was powered by the Rolls-Royce Merlin II engine and made its maiden flight on the 18th May 1939 with the large heavy four gun turret mounted within the fuselage just behind the cockpit, this was to be the aircraft's only armament, although the turret could be fixed to fire forward above the propeller. However, the weight and high degree of drag caused by the protruding section of the turret was to limit both the manoeuvrability and speed of the Defiant.

The first production Boulton Paul Defiant was flown on the 30th July 1939 and would originally operate as a day fighter. With a top speed of 304 mph, range of 465 miles, service ceiling of 30,350 ft and armament of four 0.303-in machine-guns in a rear turret. The first deliveries of this new aircraft were made to No. 264 Squadron, who had been reformed on the 30th September 1939, with the first two arriving on the 8th December 1939. This was followed by No. 141 Squadron, who received their first Defiant on the 4th April 1940, and became the second operational Boulton Paul Defiant squadron on the 3rd June 1940. The next month saw No. 264 Squadron move to RAF Duxford on the 10th May 1940. Two days later on the 12th May 1940 No. 264 Squadron took the Defiant into battle over Continental Europe for the first time when six were in action over the Netherlands alongside six Spitfires from No. 66 Squadron.

The 19th July 1940 saw the Defiant used in the Battle of Britain (10th July 1940 - 31st October 1940) for the first time when No. 141 Squadron were tasked with convoy protection. However after being bounced by Messerschmitt Bf 109s they lost six of the nine aircraft, with the loss of ten aircrew killed, this would be the only Defiant day fighter sortie performed by the squadron. No. 264 Squadron also saw action during the Battle in August but by now the Luftwaffe pilots had worked out that if they attacked the Defiant head on they could do so with complete immunity. This saw the aircraft suffer increasing losses, and as a result they would no longer operate as day fighters from the 28th August 1940.

The Boulton Paul Defiant now operating mainly as a night fighter began regular patrols on the 13th September 1940, which led to the Defiant NF Mk IA and a number of aircraft were installed with a comparatively new and secret Airbourne Interception Mk. IV radar. It was in the night fighter role that the Defiant was to have success as part of Britain's night defences in the winter of 1940-41. During this period they were to shoot down more enemy aircraft than any other contemporary night fighter. With the introduction of newer aircraft for night fighting No. 264 Squadron would be the last to operate the Defiant in this role, until May 1942, when they were replaced by the de Havilland Mosquito Mk II.

The aircraft would be involved in one of the more mysterious episodes of the Second World War (1939 - 1945) when on the 10th May 1941 a pair of Defiants from No. 141 Squadron were sent to intercept an aircraft. Despite pursing the aircraft they were unable to catch it. It would later transpire that the aircraft was a Messerschmitt Bf 110 flown by Rudolf Hess, the Deputy Fuhrer to Adolf Hitler.

A pair of Defiant Mk Is fitted with a more powerful Rolls-Royce Merlin XX engine, and featuring changes such as an improved rudder with a greater area, modifications to the fuel systems, engine cooling and increased fuel capacity, would be used as Defiant Mk II prototypes. With the 20th July 1940 seeing the first prototype fly. The Defiant Mk II had a top speed of 313 mph, range of 480 miles and a service ceiling of 30,348 ft. Armament was four 0.303-in machine-guns in a rear turret. The 29th August 1941 saw No. 264 Squadron take delivery of the first examples. Over 200 were built, although many were converted to target tugs later on, and a number were built as dedicated target tugs. In this role they were used both at home and in the Middle and Far East. Defiants were also used for air-sea rescue, carrying air dropped dinghies.

The Boulton Paul Defiant would achieve the feat of becoming, not only the RAF's first electronic countermeasures aircraft, but the world's first. It would be equipped with either Mandrel, which jammed the German early warning radar known as Freya. The other was known as Moonshine, this made a raid appear on German radar larger than it really was. It was in the ECM role on the 17th July 1943 that four Defiants from No. 515 Squadron flew the types final operational sortie.

A Defiant TT Mk I would be sent to Martin-Baker on the 11th December 1944 so it could be used by the company to test their ejection seats. The first dummy trials started on the 11th May 1945. Martin-Baker also received a second Boulton Paul Defiant which they used to test their ejection seats. The Air Ministry would also conduct their own trials using a Defiant until March 1947.

February 1943 saw Defiant production end and in total 1,064 had been built.

Technical Details

Click on the aircraft image to view a larger version.

Top Speed Range Service Ceiling Armament
Defiant Mk I 304 mph 465 miles 30,350 ft four 0.303-in machine-guns
Defiant Mk I side profile image
Defiant Mk II 313 mph 480 miles 30,348 ft four 0.303-in machine-guns
Defiant TT Mk III Target tug.


Click on a photo to view a larger version.
Defiant Mk I

See This Aircraft

(C) = Cockpit only exhibit. (F) = Fuselage only exhibit. (R) = Remains of an aircraft.

Defiant Mk I Kent Battle of Britain Museum
Defiant Mk I (R)
Defiant Mk I Royal Air Force Museum, Midlands

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