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 where during the winter of 1940 – 41 it shot down more enemy aircraft than any other night fighter.
The Boulton Paul Defiant would go on to become the world's first electronic countermeasures aircraft.
First flight 11th August 1937
Entered service 8th December 1939
Total built 1,064
In the 1930s a new tactical concept was conceived, this proposed the idea 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 inline 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's chief
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 Aircraft 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 as it had no forward firing guns. 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 the first deliveries of this new aircraft were made to No. 264 Squadron, who had been re-formed on the 30th September 1939, with the first two arriving on the
8th December 1939. This was followed by No. 141 Squadron, based at that time at RAF Turnhouse, who in April 1940 became the second Defiant squadron when they replaced their
Gloster Gladiators and Bristol Blenheim Mk IFs. The next month saw No. 264 Squadron move to RAF Duxford on the 10th May. Two days later
on the 12th May No. 264 Squadron took the Defiant into battle for the first time over Holland. By the end of May 1940 despite losing fourteen Defiants No. 264 Squadron had claimed a total of 65
enemy aircraft destroyed.
The 19th July 1940 saw the Defiant used in the Battle of Britain
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, and
this would be the only daylight 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 were removed from daylight operations on the 28th August 1940.
The Boulton Paul Defiant was instead moved into a new night fighter role, beginning regular patrols in September 1940, which lead 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, 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.
To try to improve the performance of the Defiant two Mk Is served as prototypes for the new Mk II version. Fitted with a more powerful Merlin XX engine whilst other changes to the aircraft saw the
rudder improved with a greater area, modifications to the fuel systems, engine cooling and an increased fuel capacity. Its top speed of 313 mph was an improvement over the Mk I as was its range of
480 miles. The Mk IIs service ceiling was 30,348 ft and armament remained the four 0.303-in machine-guns. This new Defiant was first flown in June 1940 and 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 sole 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.
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.