Originally designed as a bomber destroyer the Defiant was pressed into service as a day fighter over the beaches of Dunkirk and during the Battle of Britain. Despite early successes ever
increasing losses saw the Boulton Paul Defiant moved to night fighting where it excelled.
First flight 11th August 1937
Entered service December 1939
Total built 1,065
In 1935 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 for a two-seater fighter plane with a power operated gun turret Hawker and Boulton Paul both made submissions. Hawker's prototype was called the
Hotspur, however this aircraft was not to compete against the two which were ordered from Boulton Paul. This was mainly because there was no producing capacity left in the Hawker factories due to
orders for the Hawker Hurricane meaning the Hotspur prototype was abandoned.
The first prototype of Boulton Paul's, now called the Defiant, made its initial flight on the 11th August 1937, although an order for 87 aircraft had been placed four months before on the 28th April.
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 second prototype had a Merlin II engine). Both of the prototypes had 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 examples arriving
during December 1939. This was followed by No. 141 Squadron who in April 1940 became the second Defiant squadron when they replaced their
Gloster Gladiators. 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.
In its first operations it achieved complete surprise as Luftwaffe pilots either mistook the Defiant for a Hurricane
or assumed it was armed with forward firing guns like most conventional fighters. By the end of May 1940 they 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 losing six of the nine aircraft dispatched this would be the only daylight sortie
performed by the squadron. 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 (AI) 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 when on the 10th May 1941 a pair of Defiants from No. 141 Squadron, Ayr 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. Also serving
in other roles Defiants were used for air sea rescue, carrying air dropped dinghies, and some also carried the Mandrel noise jammer to co combat the German early warning radar.
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.
During its peak as a night fighter 13 RAF squadrons were using Defiants. Its removal from combat duties in 1942 was followed a year later by production being ceased. In total 1,065 had been built.