Flawed design or unfairly treated by history? The Boulton Paul Defiant assessed

The Antique Airshow
Nov 10
8 min read

The Boulton-Paul Defiant Turret Fighter:

In the 1930s, a new type of tactical thinking emerged within Britain. It was believed that if Germany were to bomb Britain, it would do so via unescorted, long-range bombers operating from airbases within Germany. The fighters of the early 1930s lagged behind the fast and modern bomber designs of the era and thus would not have the ability to escort bombers from Germany to Britain and back.

The counter to this perceived threat was a fighter with all its firepower concentrated in a turret. Such an aircraft could destroy bombers by attacking from below or from the side. Another proposed benefit of concentrating the firepower in a turret was that the pilot could focus solely on flying and positioning the aircraft, while the gunner managed the attack. Lastly, the turret allowed a greater defensive and offensive firing arc. It was this tactical theory that would spawn the infamous Boulton Paul Defiant.

Defiant Origins:

The Boulton Paul Defiant originated in Air Ministry Specification F.9/35 of June 1935, which called for a two-seater fighter with all its armament concentrated in a power-operated turret. It was expected that, even with a turret, the aircraft’s performance would only be slightly below that of the new single-seat fighters then emerging.

Designs were submitted by Hawker, Fairey, Supermarine, Gloster, Armstrong Whitworth, and Boulton Paul. Boulton Paul’s submission, designed by John Dudley North, was to incorporate a French-designed turret that the company was already building under license for their Overstrand bomber. The turret housed four .303-calibre machine guns. In October 1935, the Air Ministry ordered two prototypes of the Boulton Paul design (known as the P.82) and the Hawker design (known as the Hotspur).

Before the prototype had even flown, an order for 87 Defiants was placed in April 1937. The prototype, minus its rear turret, made its first flight on 11 August 1937 with Boulton Paul’s chief test pilot Cecil Feather at the controls. It was powered by a Rolls-Royce Merlin I engine. On 7 December, the prototype was sent to the Armament Experimental Establishment at Martlesham Heath for trials. Without its turret installed, it performed well, reaching 320 mph. This was followed by an additional order for 202 Defiants in January 1938. In February, the turret was finally installed on the prototype. The added weight and drag significantly reduced the Defiant’s speed and manoeuvrability.

Perhaps now is a good time to mention that the Defiant’s rival, the Hawker Hotspur, never made it into production. After encountering delays, it eventually flew on 14 June 1938—ten months after the Defiant—and the project was subsequently abandoned.

Testing of the Defiant revealed a few faults, which were addressed in the second prototype. Powered by a Merlin II engine, it first flew on 18 May 1939. The first production aircraft took to the air on 30 July, and was very similar to the second prototype, but equipped with the upgraded Merlin III engine. In October, mock combat trials were held between the Defiant, Hurricanes of No. 111 Squadron, and a Bristol Blenheim bomber. The Defiant performed well against the Blenheim but was no match for the Hurricanes, being easily outmaneuvered and outperformed. Nevertheless, the aircraft was pressed into service.

the Boulton Paul Defiant prototype 1937 — The Boulton Paul Defiant prototype in 1937. Source: Imperial War Museum

The Boulton Paul Defiant in combat:

Production delays meant that, by the outbreak of the Second World War, only three Defiants had been delivered to the RAF. The first squadron to receive them was the newly formed No. 264 Squadron, taking delivery of its first three aircraft on 8 November 1939. The following months, as No.264 worked up to operational status, training was undertaken and tactics finalised. One tactic, which would be effectively utilized in the skies over France in 1940, was the formation of a defensive circle or spiral when bounced by German Bf.109s. This allowed for the Defiants to cover each other and return fire at the German aircraft from whatever direction they attacked. By mid-March 1940, No. 264 Squadron was declared operational.

On May 10 1940, the Germans began their invasion of the low countries. Two days later on May 12, the Defiant’s of No.264 Squadron engaged the enemy for the first time. On a patrol over the Netherlands alongside Spitfires of No. 66 Squadron, the Defiants shot down a Junkers Ju 88 and a Heinkel He 111. Throughout May, flying from bases within England, the squadron flew patrols over the Netherlands and, following the surrender, over the beaches of Dunkirk. They proved effective, claiming numerous victories over Luftwaffe bombers and fighters. On May 29 1940, the squadron claimed 37 aircraft destroyed with no loss of aircraft - though one gunner who bailed out was never seen again. It is believed the true total is lower, but nonetheless the day was a success for No.264 Squadron. By the end of May, when the squadron was withdrawn to rest and reequip, the squadron had claimed 64 German aircraft shot down from 174 sorties, at the cost of 14 Defiants.

The second squadron to re-equip with Defiants was No.141 Squadron, entering combat during the Battle of Britain. At the time based at Hawkinge, their first action occurred on the 19th of July 1940. The squadron was scrambled and directed to intercept a force of BF.110 attacking shipping in the English Channel. Nine Defiants made it in the air and flew to intercept, however were bounced by BF.109s. In the ensuing fight only two of nine Defiant’s survived the attack and ten aircrew were killed. In return only four BF 109’s were claimed to be shot down. The Defiant’s were woefully unmatched against the German fighters. Additionally, throughout the fight the Defiant’s never entered a defensive circle or spiral that had been effectively used in France to hold off enemy aircraft. This would be No.141 Squadron's only day time operation with the Defiant, as shortly after this they were withdrawn to Scotland. Consequently, No.264 Squadron were also moved further North. Aviation Author Alec Brew concludes that it was this action that “has tainted the reputation of the Defiant to this day.”

On August 22 1940, No.264 Squadron moved back south and into the thick of action. No.141 Squadron were kept in Scotland. For the remainder of August No.264 squadron would be actively involved in the Battle of Britain being involved in numerous intercepts. Here it faired with a variety of results. Between 22 and 28 August, the squadron had 15 confirmed enemy bombers (and one unconfirmed), for the loss of five pilots, nine air gunners and eleven aircraft. As Michael Bowyer wrote in Profile Publications: The Boulton Paul Defiant, the crews “had put up a gallant resistance.” By the end of August, No. 264 Squadron was withdrawn to Duxford, and daylight operations by Defiants effectively ceased. The type would henceforth serve mainly as a night-fighter.

Defiant Mk.Is of No.264 Squadron during August 1940.

The Boulton Paul Defiant as a night fighter:

The Defiant was found to be quite useful as a night-fighter. On 1 July 1940, a No. 141 Squadron aircraft flew the type’s first night patrol, and on 15 August, a No. 264 Squadron Defiant achieved its first night victory. In mid-September, the Blitz began and the Defiant became an important piece in defending British airspace from the German bombers. When the Blitz began in mid-September, Defiants became an important part of Britain’s night defences, claiming more enemy aircraft than any other type during the winter of 1940–41.

By the end of 1940, three additional squadrons (including the Polish No. 307 Squadron) had re-equipped with Defiants. By March 1941, this had risen to a total of seven squadrons flying the Defiant.

Night-fighter Defiants equipped with Airborne Interception Mk IV radar were designated NF Mk IA. Next came the Defiant Mk II, powered by the more powerful Merlin XX engine which increased top speed to 310mph. The Mk II also included other modifications such as a greater area of rudder and increased fuel capacity, while being equipped with the more advance AI Mk VI radar. Mk IIs began to enter service in September 1941.

As more capable night-fighters like the Bristol Beaufighter and de Havilland Mosquito became available, the Defiant was gradually phased out. No. 264 Squadron was the last to convert, trading its Defiants for Mosquitos in May 1942—bringing an end to the Defiant’s fighter career.

A Defiant Mk I Night Fighter of No.256 Squadron RAF. Source: Imperial War Museum

Additional roles of the Boulton Paul Defiant:

The Defiant story did not end there though, with the type fulfilling a range of secondary roles.

The Defiant would become the world’s first electronic countermeasures aircraft. It was fitted to carry two types of jamming equipment: Mandrel, which jammed the German Freya early-warning radar, and Moonshine, which created false echoes to make British bomber formations appear larger on radar. No.515 Squadron was the sole unit that utilized the Defiant in electronic countermeasures, flying its first mission on 17 August 1942 and the last on 17 July 1943.

Next, Defiants served in air-sea rescue roles, beginning in March 1942 with No. 281 Squadron. However, their high stalling speed and wide turning circle made them less than ideal. Most were worn-out airframes, and by the end of 1943 the type had been phased out of this duty.

From 1940, Defiants were also used by Operational Training Units.

The final role the Defiant was utilized in was as a target tug. As a target tug, the turret was removed, and a winches, target stowage box and observer’s position were added. In July 1941, 150 of these Defiants were ordered under the designation T.T Mk I. Powered by the Rolls Royce XX engine, the prototype flew for the first time in January 1942.

Target tug Defiants were heavy and slow, reaching only about 250 mph. An improved T.T Mk II, powered by the Merlin 24 engine, was designed but never built. Instead, surplus Mk Is were converted into T.T Mk III aircraft. Between 1943 and 1944 it is believed that 224 Defiant Mk Is were converted to target tugs, mainly by the firm Reid and Sigrist. Defiant Mk IIs were also converted to T.T Mk I standard. Defiant target tugs served with both the RAF and Fleet Air Arm worldwide, including in the Middle East, India, and Africa. A tropical version, featuring a large filter under the nose, was developed in 1943–44.

A few Defiant T.T Mk Is were later used by Martin-Baker and R. Malcolm Ltd. to develop ejection seats. On 10 August 1945, a Defiant was used for the first ground-based ejection seat test. On 11 May 1946, it made British aviation history when a dummy was successfully ejected in flight—the first airborne ejection seat test in Britain. The Air Ministry is believed to have kept a Defiant for ejection-seat trials until March 1947.

Boulton Paul Defiants in flight over Sierra Leone after taking off from HMS Spurwing. — Defiants in flight over Sierra Leone after taking off from HMS Spurwing.

Conclusion:

Production of the Defiant ended in 1943, with a total of 1,064 aircraft built. Though outclassed by the Hurricane, Spitfire, and enemy Bf 109, it achieved early successes and proved particularly effective against bomber formations—the very role for which it was designed. As a night-fighter it proved to be more than adequate. Ultimately, the aircraft was designed to satisfy tactical thinking that was outdated and obsolete by the beginning of World War Two. As a result, the aircraft was destined to fail. Still, it would end combat sorties with 155 victories from 5,200 missions flown. The Defiant also served with the Royal Australian Air Force, Royal Canadian Air Force, and Polish Air Force. Though far from the best fighter of the war, Defiant crews fought tenaciously and bravely.

Today, only one complete Boulton Paul Defiant survives, preserved at RAF Cosford. The wreckage of another can be seen at the Battle of Britain Museum, Hawkinge, while a project to reconstruct a Defiant cockpit from original parts is underway at the Tettenhall Transport Heritage Centre, Wolverhampton.

A full-scale replica built by the Boulton Paul Aircraft Heritage Project is now on display at the Battle of Britain Museum, Hawkinge, where it remains to this day.