WWII Tech Pubs Briefing

Written by
Jonathan Charles

12th May 1940. Boulton Paul Defiants of 264 Squadron provide an unpleasant shock to Bf 109s over the Dunkirk sector. Initially the Defiants obtained complete tactical suprise, a situation that the Luftwaffe were quick to reverse. Defiants later suffered horrific losses in combat.

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Overview

In 1935, the British Air Staff issued specification F.9/35, for a new two-seat Rolls Royce Merlin powered fighter. Unusually it was to have no forward firing armament, instead carrying a new Boulton Paul four-gun powered turret, recent testing of which had largely inspired the project. The new fighter was intended to counter the growing threat of German bombers attacking Britain from across the North Sea. Since such raids were considered to be beyond the range of enemy escort fighters, the new turret fighter would be free to closely engage the enemy bombers from their defensive blind spots. Seven F.9/35 proposals were submitted, but only Hawker and Boulton Paul were awarded contracts to develop their designs into prototypes.

Boulton Paul’s P.82 was designed by a team led by J. D. North and flew first, in August 1937. It was a compact low wing monoplane of only 39 ft 4 in (11.99 m) span, powered by a Rolls Royce Merlin I of 1,030 hp (768 kW) driving a three-bladed two pitch propeller. The five-piece wing had two spars and like the fuselage was of flush riveted stressed skin construction. Its centre section contained the non self-sealing fuel tanks, split flaps, and wide track retracting undercarriage.

Despite being slightly smaller and having the same engine as the Hawker Hurricane, it was some 22% heavier and 25 mph (40 km/h) slower. This was mainly due to the weight and drag of the Boulton Paul Mk IID turret mounted behind the cockpit. Armed with four Browning .303 in (7.7 mm) machine guns, this was powered in traverse and elevation by an internal electrically driven hydraulic pump. There was also a reflector gun sight and an interrupter mechanism to prevent the gunner shooting holes in his plane. To reduce its drag, wooden fairings were fitted in front and behind of the turret. In combat, these were retracted pneumatically into the fuselage to allow a full 360 degrees of traverse.

Hawker’s Hotspur flew nine months after the P.82. A much larger aircraft of 47 ft 10 in (14.59 m) span, it employed Hurricane outer wing panels on an enlarged centre section. Despite its larger size, the Hotspur was both lighter and 10 mph (16 km/h) faster than the P.82, and its much lower wing loading gave it far superior manoeuvrability. However Hawker was by this time stretched to capacity building Hurricanes, so the Hotspur was dropped and the contract went to Boulton Paul’s P.82, which was now named the Defiant.

Development delays meant it was December 1939 before the Defiant entered RAF service. Engine and turret problems then delayed its operational debut with 264 squadron until May 1940. On the 14^th six of 264’s Defiants engaged a force of Ju 87s off the Dutch coast, quickly claiming four of them before losing five of their number to escorting Bf 109s. Further operations over the Dunkirk evacuation at the end of the month followed the same pattern: some successes against bombers, but heavy losses to escorting fighters. When mistaken for the similar looking Hurricane the Defiant occasionally gave enemy fighters a nasty surprise, particularly when 264 was able to fly in mixed formations with Hurricanes. Yet on the whole they were considered an easy kill. The Defiant was far less manoeuvrable than the German fighters and its guns were unable to depress below horizontal or fire to the front. Realizing this, the enemy fighter pilots attacked from below the Defiant’s tail or from directly ahead. After losing seven aircraft on the 31^st, the remnants of 264 were withdrawn to the north of England to regroup.

Although 264 had been almost completely wiped out in a little over two weeks of operations, they had claimed 65 kills, including 37 over Dunkirk on the 29^th May. These figures were vastly inflated by the effect of several gunners in a formation claiming the same kill. Yet at the time they seemed impressive enough for a second Defiant squadron, No. 141, to be deployed in Kent during the Battle of Britain. This squadron’s first and last daylight combat was a disaster. On July 18^th Bf 109s shot eight out of a formation of nine aircraft down. Then in August a replenished 264 squadron had to be stood down after just four days of costly operations in the south. By the end of August over half the 120 Defiants built had been lost in combat, giving the RAF no choice but to withdraw them from daylight operations.

The lesson having finally been learnt, Defiants were redeployed as night fighters just as the Luftwaffe began its nightly Blitz of British cities. Lacking endurance, performance and AI radar, they were rarely able to find the enemy bombers. However when by luck an interception was made the Defiant was an effective killer. It could silhouette the enemy aircraft against the moon and attack while hidden in the gloom below. Mk IA aircraft fitted with compact Mk IV AI radar began appearing in early 1941, just as the Blitz was ending. Despite the lack of targets, by 1942 eleven RAF and two RCAF squadrons were Defiant equipped. Four of them flew the new Mk II, a specialised night fighter with a 1,280 hp (955 kW) Merlin XX and 50% more fuel. The new engine increased the Mk II’s speed to 315 mph (597 km/h), but it was not enough. By September 1942 all the night fighter squadrons had been reequipped with Beaufighters, Havocs or Mosquitoes.

Most Defiants were converted into TT Mk I or III target tugs, with the turret replaced by towing gear. In this capacity and as gunnery trainers, they served until the end of the war. Other uses included dropping dinghies to downed aircrew and with No 515 Squadron, electronic warfare. From October 1942 until mid 1943 this squadron used onboard Mandrel transmitters to jam enemy ground radars in the path of RAF bomber streams.

The failure of the Defiant led to the cancellation of its replacement, the P92. This was to have been a twin-engine aircraft with a turret mounting four Hispano 20 mm guns. Still, the idea of a turret fighter died hard with some in the RAF; a Defiant with a single Hispano 20mm gun it its turret was tested, as was a Beaufighter with the original four-gun turret. Neither was developed to production and Boulton Paul’s turrets were instead fitted to heavy bombers like the Halifax.

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Variants

* Converted from existing airframes.

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Specifications

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