Fighter Command’s Order of Battle for August 8, 1940 shows 30 squadrons equipped with the Hawker Hurricane I,19 squadrons of Supermarine Spitfire Is, two flying the two-seat Boulton Paul Defiant turret fighter and six squadrons of twin-engined Bristol Blenheim IF’s. One squadron was equipped with ancient Gloster Gladiator biplanes, but saw no action during the period of the Battle of Britain. In the hectic weeks of the Battle itself, there was little time to re-equip the squadrons in the front line and, other than the early withdrawal of the Defiants, the disposition of the RAF’s fighters remained substantially unchanged up to the end of the Battle. Thus, it was the Hurricane that bore the brunt of the fighting in the air, and was responsible for the major share of losses inflicted on the Luftwaffe, although the Spitfire was to capture the public imagination as the fighter par excellence.
Both Spitfire and Hurricane had been conceived at a time when ‘fighter’ meant, to the RAF, a single-seat, fixed undercarriage biplane with an armament of four 0.303in machine guns and no greater concession to fighting efficiency than an enclosed cockpit for the pilot. Advances in aerodynamics, aero engineering and power plant development in the mid-’thirties, however, opened up the possibility of major improvements in performance and combat ability – improvements that were quickly seized upon by Reginald Mitchell and Sydney Camm in their positions as chief designers, respectively, of Supermarine and Hawker Aircraft.
Often going beyond the Air Ministry’s ‘official’ requirements as set out in a succession of Specification documents in the early ’thirties, Mitchell and Camm both produced low-wing monoplanes with enclosed cockpits, retractable undercarriages and eight-gun armament, powered by the then new Rolls-Royce Merlin liquid-cooled in-line engine, In design terms, the Hurricane was a little older than the Spitfire, and later in the war it would prove less amenable to development. What mattered in 1940, though, was the fact that it was available in useful numbers, was easy to fly, rugged and able to sustain considerable damage and still return to base. Slower in the climb and in level speed than the nimble Spitfire, the Hurricane was well suited to the task of intercepting the relatively slow bomber formations, leaving the Spitfires to deal with the escorting fighters. This division of roles also helped to account for the greater success of the Hurricane in kill-to-loss ratio during the Battle.
Design of the Hurricane had begun in 1934, and its first flight had been made, from Hawker’s establishment within the confines of the historic Brooklands motor racing circuit at Weybridge in Surrey, on November 6, 1935. Sydney Camm’s design team at nearby Kingston upon Thames already had long experience of fighter design for the RAF, and drew heavily upon this experience to produce what was at first seen as a ‘Monoplane Fury’ – the Fury being the elegant biplane that still epitomised the equipment of Fighter Command upon its formation within the RAF in July 1936. Such advanced features as an enclosed cockpit and retractable undercarriage were combined with traditional methods of construction using a tubular metal structure and fabric covering, that meant that the Hurricane could be easily and rapidly produced in existing facilities – an advantage not enjoyed by the Spitfire with its advanceds stressed-skin construction and complex shapes.
In February 1936, the prototype Hurricane (as yet unnamed), powered by an early Merlin C producing 990hp and driving a Watts fixed-pitch two-bladed wooden propeller, was tested at the Aircraft and Armament Experimental Establishment (A & AEE) at Martlesham Heath, giving Service pilots their first opportunity to experience the improvements in performance and handling that were to become available. At a weight of 5,672lb (2,572kg), the prototype demonstrated a speed of 315mph (506km/h) at the Merlin’s rated altitude of 16,200ft (4,937m) with 6lb/sq in boost. After taking off into a 5mph (8km/h) wind with a run of 795ft (242m) to reach the 81mph (130km/h) lift-off speed, the Hurricane climbed to 15,000ft (4,570m) in 57 minutes and to 20,000ft (6,100m) in 8.4 min. Service ceiling was 34,500ft (10,515m) and the estimated absolute ceiling was 35,400ft (10,800m).
Convinced that the RAF would buy the new fighter in the prevailing mood of rearmament, the Hawker company decided, in March 1936, to proceed with the production drawings and to make plans for large scale production. Three months later, that action was vindicated when the Air Ministry confirmed Hurricanes were to be included in its expansion Plan F (which also provided for 300 Spitfires). By the time the Battle of Britain began, every single fighter in the hands of the RAF counted, and the early launch of Hurricane production had helped to ensure that just enough machines were in fact available to Fighter Command.
Even so, meeting the RAF’s rapidly expanding needs proved to be no simple matter and the Plan F target of 600 Hurricanes to be delivered by March 1939 was missed by some six months. There had been a succession of relatively minor but time-consuming problems with prototype development, especially related to the Merlin and the early intention to fit the Merlin F (Mk I) in the production Hurricane was changed to make use of the improved Merlin G (Mk II) – which required a redesign of the installation and the front fuselage profile before production could begin. The cockpit canopy also produced its share of problems, with five failures recorded on the prototype before a satisfactory design was evolved.
The first production Hurricane I flew at Brooklands on October 12, 1937, fitted with an early example of the Merlin II and at a weight of 5,459lb (2,476kg). The second aircraft was in the air six days later, and production deliveries then built up rapidly. Meanwhile, during 1936, the prototype had been fitted with the planned armament of eight Browning machine guns and first firing trials had been made. Design of a metal-covered wing was in hand, but to avoid production delays the Hurricane I retained the fabric-covered wing, in which the guns were grouped in two quartets, positioned to fire just outside the propeller disc and therefore requiring no complicated synchronisation gear. Each gun was provided with 300 rounds, and the two batteries of guns were harmonised to converge at 650 yards (594m) – although with experience this distance was to be reduced eventually to 200 yards (183m).
Service use of the Hurricane began with No. 111 Squadron at Northolt, which was fully equipped by February 1938. By July 1939, 12 regular squadrons were flying the Hurricane I, to be followed by six Auxiliary Air Force squadrons, converting to the fighter role from bomber or army cooperation in which the AAF had previously operated. Powered by the Merlin II and still using the two-bladed fixed-pitch wooden propeller, the standard Hurricane I in 1938 had a tare weight of 4,732lb (2,146kg) and a normal loaded weight of 6,056lb (2,747kg) when carrying full ammunition and 77.5 Imp gal (352 1) of fuel. This gave a range of 340 miles (547km) at 275mph (442km/h) at 15,000ft (4,575m), but with full tankage of 97 Imp gal (441 1), the max take-off weight was 6,202lb (2,813kg) and the range increased to 680 miles (1,094km), with an endurance of 4.2 hrs, at the economical cruising speed of 162mph (261km/h). Max speed was 312mph (502km/h), the time to 15,000ft (4,575m) was 7 min and service ceiling was 33,000ft (10,058m). The take-off distance to clear 50ft (15.2m) was 1,800ft (549m) at normal weight and 1,890ft (576m) at max weight.
A second major version of the Hurricane would make its first flight on June 11, 1940 and, as the Hurricane IIA, would begin to reach the squadrons on September 4, 1940, just too late to figure effectively in the Battle of Britain itself. Thus, those squadrons engaged throughout August and most of September were still mounted on the Hurricane I, albeit somewhat improved by comparison with the 1938 delivery standard. An armoured bulkhead had been introduced forward of the cockpit and, when Hawker Aircraft’s second production batch began leaving the assembly line in September 1939, a bullet-proof windscreen had been standardised. This batch also adopted the Merlin III engine which featured a shaft capable of taking either a Rotol or de Havilland three-bladed constant-speed propeller. While some Hurricanes were produced during 1939 with the DH two-position propeller, a major conversion programme was started on June 24, 1940 to fit the Rotol constant-speed unit which allowed the pilot to select optimum engine power for the various stages of flight. Significantly improving the Hurricane I’s climb performance, Rotol propellers had been fitted to all Hurricanes by mid-August 1940. With the 81st Hurricane of the second batch, the fabric-covered wing finally gave place to an all-metal stressed-skin wing and, on February 2, 1940 the first Hurricane with rear armour protection for the pilot was flown.
Before battle was joined, the fact that the Hurricane was inferior in most performance respects to its principal German opponent, the Messerschmitt Bf 109E, had been accepted. The Bf 109E was faster at all altitudes, and could out-climb and out-dive the Hurricane with ease. Thus, if the German pilot elected to break off the engagement, the pilot of the Hurricane was powerless to pursue his erstwhile opponent. But in low-altitude manoeuvrability and turning circle at all altitudes the Hurricane had the upper hand and, provided the Bf 109E did not join combat with an altitude advantage, the Hurricane was its match. Apart from its performance inferiority, the Hawker fighter was not found wanting, and its sturdier structure enabled it to withstand battle damage that would have rendered its antagonist hors de combat.
The Hurricane’s admitted shortcomings in performance compared with that of the Bf 109E led to it being allocated the primary task of dealing with the Luftwaffe bomber formations – which seldom operated much above 16,000 - 17,000ft (4,877 - 5,181m) – leaving the faster-climbing Spitfires to keep the escorting Bf 109Es occupied. In the heat of battle it rarely proved possible to co-ordinate the attacks of both Hurricane and Spitfire formations in such an optimum fashion, however, and all too frequently Hurricanes intercepting a bomber formation were attacked from above by escorting Bf 109Es.
By the end of 1939, the RAF had received more than 600 Hurricane Is and production was at the rate of 100 a month – a figure that had been more than doubled by the middle of 1940. Losses had been suffered in France, totalling almost 300 machines and many of the RAF’s most experienced pilots, but the massive production effort – in which Gloster joined with Hawker, flying its first Hurricane I at Hucclecote on October 20, 1939 – and the herculean task of repairing those aircraft damaged during the Battle of Britain itself ensured that ‘the Few’ did not run out of fighters in 1940. By the end of the Battle, some 1,700 Hurricanes had served with Fighter Command, and 696 had been lost to the Service, either permanently or temporarily, in the two months of fighting.
Had the Battle continued longer, the Hurricane IIA would have been able to reduce substantially the margin of performance superiority enjoyed by the Bf 109E. With a l,260hp Merlin XX engine, this mark could reach 20,000ft (6,095m) in 8.2 minutes and had a maximum speed of 342mph (550km/h) at 22,000ft (6.705m). Soon to have the benefit of heavier firepower – either 12 machine guns or four cannon – the Hurricane IIs would continue to do battle with the Luftwaffe, by night as well as day, in the months that followed the Battle of Britain itself.
Like the Hawker team, the design staff of the Supermarine Aviation subsidiary of Vickers (Aviation) Ltd had become interested in the early ’thirties in the RAF’s need for a new fighter, and by 1934 was actively engaged in the design of an ‘experimental high-speed single-seat fighter’. Known as Design 300, this was conceived by the team led by R. J. Mitchell and based more on experience of high-speed flight obtained through the design of the Schneider Trophy-winning seaplanes than upon familiarity with fighter design. Ordered by the Air Ministry as a single prototype in December 1934, the Supermarine 300 – forerunner of the Spitfire – owed more to the instinctive creativity of a brilliant designer than to the intelligent application of experience, as exemplified by the Hurricane.
Be that as it may, the result was an aircraft that was of similar configuration to the Hurricane, similarly powered and armed and first flown some six months after the Hawker prototype, on March 5, 1936, at East-leigh near Southampton. If the Hurricane was a reliable workhorse – albeit a thoroughbred – the Spitfire was a ballerina, an impression fostered by the powder-blue finish adopted for the prototype and enhanced by the frail, narrow-track undercarriage. Outnumbered by the Hawker fighter in the Battle of Britain, the Spitfire was destined to outproduce, outfly and outlast the Hurricane. But it was in 1940 that (in the words of test pilot Jeffrey Quill) ‘the little Spitfire somehow captured the imagination of the British people at a time of near despair, becoming a symbol of defiance and of victory in what seemed a desperate and almost hopeless situation’.
The Spitfire prototype went to the A & AEE in July 1936, at which time it had a Merlin C driving a de Havilland fixed-pitch two-bladed wooden propeller. It was tested at a weight of 5,322lb (2,418kg), and was found to have a speed of 349mph (561km/h) at 16,800ft (5,120m) and 324mph (521km/h) at 30,000ft (9,145m). It took 17 minutes to reach the latter altitude and 5 min 42 sec to get to 18,000ft (5,485m), and had a service ceiling of 35,000ft (10,670m). The performance edge over the Hurricane was thus already evident, and handling was good, too, the Service pilots at the A & AEE reporting that the prototype was ‘simple and easy to fly and had no vices’. It had well harmonised controls, which appeared to give an excellent compromise between manoeuvrability and steadiness for shooting. The report concluded that the Spitfire (as the Supermarine 300 was to be named before it entered service) could be ‘flown without risk by the average fully trained service fighter pilot’.
One of its most endearing qualities, evident from the prototype onwards, was its extremely docile behaviour at the stall, particularly under conditions of high g. On the debit side, longitudinal stability was a matter of some concern from the start, and called for a constant development effort as later marks were introduced. Of more concern during the period of the Battle of Britain were the high lateral stick forces encountered at the upper end of the speed range, and not overcome until modified ailerons were introduced in 1941.
In accordance with the provision of Expansion Plan F, the Air Ministry ordered 310 Spitfire Is on June 3, 1936 defining a standard of aircraft that was generally similar to the prototype. Powered, like the contemporary version of the Hurricane, by a l,030hp Merlin II, the first production aircraft flew on May 14, 1938, at Eastleigh, where the final assembly line was fed by the manufacturing centres at Woolston and Itchen, near Southampton.
Like Hawker, Supemarine failed by some six months to meet the Plan F target of delivery completion by March 1939. The problem was that the Spitfire, which was of all-metal stressed-skin construction, was not a simple aeroplane to build, the wing leading-edge being especially diffficult. As time went by, and in particular after the Supermarine works in Southampton had been heavily bombed in September 1940, Spitfire production would be dispersed widely over southern England and would bring 65 different manufacturing units into play.
That development was still well in the future in August 1938, however, when No. 19 Squadron at RAF Duxford received two early production Spitfires and began a 400-hour intensive flying trial. Two more squadrons received Spitfires in 1938 and, by September 1939, another four Regular units were flying the Supermarine fighter, and four AAF squadrons were equipped or equipping.
Like the early Hurricanes, the first Spitfires off the assembly line had the Merlin II engine driving a two-bladed fixed-pitch wooden airscrew. They attained 352mph (566km/h) at 19,000ft (5,790m) a maximum climb rate of 2,420ft/min (737m/min), and an altitude of 20,000ft (6,100m) in 9.4 minutes. With the 78th production aircraft, the wooden two-blader gave place to a de Havilland Hamilton two-pitch three-bladed metal propeller which, although incurring a weight penalty and having only a marginal effect on level speed, bestowed a significant improvement in the climb. No bullet-proof windscreen or armour was initially fitted, and although standard armament was envisaged as eight wing-mounted 0.303in Browning guns each with 300 rounds of ammunition, a shortage of these weapons led to the installation of only four guns each in early machines. Later, the introduction of a bullet-proof external windscreen was to be followed by provision of a 6mm armour plate behind the pilot’s head. After pilots on the first squadron had complained that they banged their heads on the flat roof of the cockpit canopy, a ‘humped’ canopy was introduced, giving the Spitfire its characteristic profile.
With the DH two-position propeller, the Spitfire I had a tare weight of 4,517lb (2,049kg) and operated at a normal loaded weight of 5,844lb (2,651kg). It had a maximum speed of 346mph (557km/h) and cruised at 304mph (489km/h) at 15,000ft (4,570m). The time to that altitude was 6.85 min and service ceiling was 30,500ft (9,300m). From a standing start, it reached 50ft (15m) above the ground in a distance of 1,605ft (489m), but required almost 300ft (91m) more than this distance to come to a stop, from the same altitude. The normal range of 415 miles (668km) included a 15-min allowance for take-off and climb, and could be extended to more than 600 miles (965km) by reducing the cruising speed to 175mph (282km/h).
Like the Hurricane, the Spitfire I benefited considerably from the installation of a variable-pitch constant speed propeller, to permit which a switch was made to the Merlin III with effect from the 175th aircraft. A massive effort between June and August 1940 ensured that all the Spitfire Is then in service were fitted with the DH constant speed unit and this became standard on the later production Spitfire Is.
Evaluation of a Bf 109E-3 captured in France had already revealed that the German fighter was superior in a number of respects to the Spitfire I when originally fitted with the two-position propeller. The Messerschmitt fighter was marginally faster than its British contemporary at most altitudes, and it could out-climb the Spitfire up to 20,000ft (6,070m), above which height the British fighter enjoyed an edge, Both fighters suffered some aileron heaviness at the upper end of their speed scale. While the Spitfire possessed superior manoeuvrability at all altitudes as a result of its lower wing loading, its turning circle being appreciably smaller, the Bf 109E could always elude the Spitfire in a dive, the float carburettor of the British fighter’s Merlin engine placing it at a distinct disadvantage in this situation.
During 1939, single examples of the Spitfire I and the Hurricane I had each been fitted with a pair of 20mm cannon, with 60 rounds per gun. The Hurricane, with Oerlikon guns, was credited with destruction of a Dornier 17 on August 13, 1940, while undergoing evaluation with No. 151 Squadron, but the large-scale application of cannon armament to the Hawker fighter had to await the production of the Mk IIC, with four of the 20mm weapons apiece. The Hispano guns fitted in the Spitfire proved prone to stoppages but, after trials with the prototype installation, a batch of 30 Mk Is was similarly fitted and – with four 0.303in Brownings later added to the wing armament – were delivered from June 1940 for use by No. 19 Squadron. They were the only cannon-armed fighters operated by the RAF during the Battle of Britain. These Spitfires were designated Mk IBs, and those with the original eight-gun armament then became, retrospectively, Mk IA.
Also paralleling Hurricane development, a Mk II version of the Spitfire emerged during the course of the Battle, but reached the squadrons too late to have a decisive effect. The Spitfire IIA retained the eight-gun armament of its predecessor but introduced a l,175hp Merlin XII engine which drove a Rotol constant-speed airscrew. Whereas the Spitfire IA had its armour added in service, the IIA left the factory with armour installed. The Spitfire IIA attained a maximum speed of 357mph (574km/h) at 17,000ft (5,180m), could reach an altitude of 20,000ft (6,070m) within seven minutes of unstick and had a maximum climb rate of 2,620ft/min (798m/min). The first two squadrons converted to fly Spitfire IIs in September 1940.
Once RAF Fighter Command had discarded its outdated tactics, of which the Luftwaffe’s Bf 109E fighters took full advantage during the opening phases of the Battle, the Spitfire and its German opposite number proved remarkably evenly matched. Each possessed some characteristics superior to those of its opponent and, all things being equal, the outcome of a combat depended largely on the prowess of the pilots involved.
The production difficulties with early Spitfires were shown by comparative figures for mid-1940, when the rate was still averaging only 80 a month compared with 236 a month for the Hurricane. It would be early 1942 before the monthly output of Spitfires exceeded that of Hurricanes, and the slow build-up of production in 1938/39, combined with losses suffered by Fighter Command during the fighting over France (despite Dowding’s insistence that the precious Spitfires should not be deployed with either the AASF or the Air Component of the BEF) meant that the line was drawn exceedingly thin in August 1940.
Although outnumbered by Hurricanes in the ratio of three to two throughout the summer of 1940, the Spitfires of Fighter Command inflicted more than half the total losses suffered by the Luftwaffe in the assault on Britain – a statistic that underlines the Supermarine fighter’s particular merit in air-to-air fighting. By the very nature of the conflict, the Luftwaffe’s losses in single-seat fighters were appreciably lower than those of the RAF, however, and the Spitfire squadrons alone lost 118 fighters in combat during August, a further 55 being damaged. Adding to those lost or damaged in accidents or by enemy bombing, 237 Spitfires were deleted from the inventory during that month alone and total output of the factories engaged in Spitfire production amounted to only 163 machines. Attrition in September was even more serious, 156 being manufactured and 281 being lost to strength, of which 130 were destroyed and 80 damaged in combat. In the week ending September 13, the reserves reached their lowest ebb, with only 47 Spitfires ready for delivery in storage units.
What the outcome of the Battle of Britain would have been had the Spitfire not been available is now purely of academic interest, but what is certain is the fact that no combat aircraft ever gave better service to the country of its birth. Sadly, the same cannot be said of the Boulton Paul Defiant, the operational record of which as a day fighter can only be described as disastrous.
The concept of a two-seat single-engined fighter with all of its armament concentrated in a massive power-operated turret was based in the belief that a gunner with no responsibility for flying the aircraft and able to traverse his battery of guns through 360 degrees had more chance of hitting the enemy than a pilot who had to point his aircraft in the direction in which he wished to fire. Not properly appreciated by those who fostered this concept was the way that it divided responsibility between pilot and gunner, and required the pilot not only to fly the aircraft, but also to think in abstract terms of his gunner’s line of sight. All too easily, it would transpire, enemy fighters could creep in under cover of the blind spot beneath the tail and deliver a coup de grace.
Designed to an Air Ministry Specification under the direction of J. D. North, the P.82, as the Defiant was at first designated, was an aircraft generally similar in overall size to the Hurricane. Its all-metal structure was conventional in most respects, its only unusual feature being the method of attaching the light alloy skinning to the stringers and ribs and then attaching these to the fuselage frames and wing spars. This obviated the need to preform the skins and, by riveting them while flat and countersinking the rivets, an exceptional surface finish was obtained, helping to obviate the adverse effect on performance of the drag of the bulky dorsal turret.
The first prototype made its inaugural flight at Wolverhampton on August 11, 1937, and attained 302mph (486km/h) on the power of its Merlin I engine. Its flying characteristics were pronounced excellent. It displayed very few vices, stability was highly satisfactory, and there was practically no change of trim when the undercarriage and flaps were lowered.
An initial contract for 87 Defiant Is was placed in March 1937, and 363 more were ordered in 1938. Production was delayed, as for the Hurricane also, by the decision to use the Merlin II rather than the Merlin I, and by the time the first production Defiant flew on July 30, 1939, it was powered, in fact, by a Merlin III, the version with a standardised shaft for DH or Rotol constant-speed propellers.
In its production form, the Defiant I had an empty weight of 6,078lb (2,757kg) and a normal loaded weight of 8,318lb (3,773kg). At that weight, the maximum speed was 250mph (402km/h) at sea level and 304mph (489km/h) at 17,000ft (5,180m), the cruising speed being 259mph (417km/h) at 15,000ft (4,572m). Initial rate of climb was l,900ft/min (579m/min), the time to 15,750ft (4,800m) was 8.5 min and the service ceiling was 30,350ft (9,250m). A range of 465 miles (748km) was achieved at the quoted cruising speed.
Installed in the Defiant I as a removable, self-contained unit, the Boulton Paul A Mk IID turret mounted four 0.303in belt-fed Brownings each with 600 rounds, and its hydraulic system formed an integral part of the turret itself. The bare turret weighed 361lb (164kg), to which was added the 88lb (40kg) of the four guns, 106lb (48kg) for ammunition, and some 35lb (16kg) for the gunner’s oxygen equipment, sights, etc. Normal loaded weight at 8,318lb (3,773kg) was some 1,700lb (771kg) more than that of the similarly powered Hurricane, yet the gross wing area of the two-seater was less than that of the single-seater. It was hardly to be expected, therefore, that the Defiant would be able to compete on the score of level speed, climb rate or manoeuvrability.
This was soon borne out by comparative trials between a Defiant and a Hurricane conducted by No. 111 Squadron in October 1939, but the RAF now had a desperate need for fighters, the Defiant was just coming ‘on stream’ and there could be no going back. That same month, No. 264 Squadron formed at Sutton Bridge to be the first to fly the Defiant, with which it became operational at Martlesham Heath in 1940. Early operational results were, at best, mixed, although there were claims of remarkable successes in the last weeks of May 1940 during patrols over Dunkirk, when the Defiants were probably mistaken for Hurricanes by Luftwaffe fighter pilots who tried to attack from above and behind – a fatal error.
Even so, the operations over France took a heavy toll of No. 264 Squadron and it was back to strength only just in time for the Battle of Britain, alongside No. 141, which had formed in June as the second squadron to fly Defiants. The latter had a disastrous first engagement with Bf 109Es south of Folkestone on July 19, losing two aircraft in the first firing pass by the Luftwaffe fighters and four more when the enemy made a second attack from below and dead astern – revealing that the Defiant’s fatal weakness had been taken to heart. Thrown into battle at the end of August, No. 264 Squadron suffered a similar fate, being left with only three serviceable Defiants within a week. Both squadrons were then withdrawn from further action in the Battle, leaving the Defiant to find its forte in nocturnal operations, which it would soon be called upon to fulfil.
Night operations were also to prove to be the most suitable for the Bristol Blenheim IFs that equipped six squadrons of Fighter Command in mid-1940. The Blenheim had been designed, under the direction of Frank Barnwell, to provide the RAF with a high-speed light bomber, and a version had then been produced to provide the RAF with a replacement for the Hawker Demon turret fighter. The concept of a twin-engined multi-seat long-range fighter was to prove as flawed as that which produced the Defiant.
The first all-metal cantilever monoplane of stressed-skin construction to enter production for the RAF, the Blenheim marked the beginning of a new era in the equipment of the service after several years of acute uneasiness concerning the obsolescence of the RAF’s operational aircraft inventory. It was a cornerstone of the expansion programme, and its conversion from three-seat light bomber to heavy fighter in 1938 was prompted by what was considered, by the standards of the day, a fully adequate performance coupled with sturdiness and excellent handling characteristics.
Credited, at the time of its service introduction, with a performance that would allow it to outpace most contemporary service aircraft in all categories, the Blenheim was to be revealed wanting early in the conflict. As a bomber it proved woefully vulnerable to fighter attack, being deficient in both defensive armament and armour, and it lacked the performance necessary for a fully effective strategic fighter.
For the fighter role, the Blenheim was simply adapted from the standard Mk I bomber by the addition of a ventral pack manufactured by the Southern Railway’s Ashford workshops, containing four 0.303in Browning guns plus 500 rounds of ammunition for each weapon. This supplemented the normal armament of a single wing-mounted Browning and a Vickers ‘K’ gun of similar calibre in a B.I. Mk III semi-retractable hydraulically-operated dorsal turret. Some 200 Blenheims were modified to fighters, the first examples entering service with No. 600 AAF Squadron at Hendon in September 1938.
Powered by two 840hp Bristol Mercury VIII air-cooled radial engines, the Blenheim IF, as the fighter was designated, weighed in at 8,840lb (4,100kg) and had a loaded weight of 12,200lb (5,534kg). At that weight, the max speed was 237mph (381km/h) at sea level and 278mph (447km/h) at 15,000ft (4,572m), and the aircraft cruised at 215mph (346km/h) at 15,000ft. Initial rate of climb was l,480ft/min (451m/min), the time to 5,000ft (1,524m) was 3.9 min, and to 10,000ft (3,048m) was 8.1 min. Service ceiling was 24,600ft (7,498m), and the aircraft had a reasonably high maximum range of 1,050 miles (1,690km).
Early operational experience with the Blenheim IF dictated the provision of a reflector sight, self-sealing tanks and some armour. No. 23 Squadron undertook the first night intruder sortie of the war on December 21–22, 1939. The fact that the operation of the Blenheim fighter by day was suicidal in areas where enemy single-seat fighters were likely to be encountered in strength quickly became obvious in the course of fighting over the Continent during May and June 1940, and subsequently the Blenheim IF was restricted largely to nocturnal activities. On June 5, the Luftwaffe made its first night attack on London, and Blenheim IFs instituted a system of nocturnal patrols which, on June 18, resulted in the destruction of five bombers in conditions of moonlight.
Meanwhile, the Blenheim IF had been closely involved in the development of airborne intercept radar. A flight of three aircraft of No. 600 Squadron operating from Manston had performed operational trials with AI Mk III radar, and on the night of July 2–3 a Blenheim IF from the Fighter Interception Unit at Ford gained the first ‘kill’ by means of this equipment. Subsequently the Blenheim IF was to provide the backbone of RAF Fighter Command’s night interception force, soldiering on through the Luftwaffe’s nocturnal Blitz of 1940–41 until finally supplanted by the Beaufighter.