In 1935, with a company employing 35 people, Air Ministry Specification F5/34 called for a single-seat monoplane interceptor armed with six or eight machine-guns. A retractable undercarriage was required and an enclosed cockpit; a speed of at least 275mph (442kph) at 15,000ft (4,572m) was stipulated.
This requirement was taken up by Bristol (Type 146 835hp/622kW Bristol Perseus), Vickers (Venom 625hp/466kW Bristol Aquila), and Gloster (G.38 840hp/626kW Bristol Mercury IX). James Martin submitted the MB.2.
Funded as a private venture, Napier lent an air-cooled Dagger M.3 24 cylinder upright 'H' type engine with a rated output of 798hp at 5,500 ft / 1675m. The Dagger was not yet fully developed and suffered from lack of power yet the particular engine (No 77101) eventually installed in the MB.2 seems never to have given any trouble. Cooling air was exhausted through a controlled outlet on the fuselage underside.
Other equipment to support the MB.2 included a fixed-pitch, two-bladed wooden airscrew from the Airscrew Company and Jicwood Ltd and a set of eight Browning 0.303 in machine-guns, taken from the first batch manufactured under licence in Britain, in 1937. The build phase for the MB.2 began in March 1936, the month of the first flight by the prototype Spitfire.
Conceived for manufacture in large numbers by semi-skilled workers at low cost, the M.B.2 employed a steel-tube structure with fabric skinning, and carried an armament of eight 0.303-in (7,7-mm) Browning guns in the wings. The depth of the fuselage was virtually constant from nose to tail and vertical tail surfaces were eliminated, the rudder being hinged to the sternpost behind the elevators.
The MB.2's airframe employed the previous steel tube process, but stronger, and metal skinning was used more widely. The enclosed cockpit was placed well back and given a raised canopy with glazing fore-and-aft.
The canopy was hinged to starboard but could not be jettisoned. The rear glazed area of the hood enclosed an electrically-operated extendible crash-post which was automatically actuated when the flaps were lowered. The fuselage lines were square-cut, the depth being almost constant from engine to sternpost. A tubular cradle supported the engine which had stub exhaust ports. The metal-covered areas of the fuselage, forward of the aft cockpit area, were equipped with quick-release inspection panels held with Dzus fasteners.
The wingspan was shorter than the fuselage length, but designed to enhance stability and control in yaw. The wing was constructed as a centre-section and two outer panels. A small amount of dihedral was employed and the wing tapered slightly along the leading-edge but more acutely along the trailing edge. Blunt tips were provided, together with inset ailerons. The wing carried the eight machine-guns in two clusters of four, outboard of the undercarriage.
Martin elected to employ the rear fuselage as the fin, with the rudder hinged to the sternpost, the design lacking any conventional fin at all, in order to reduce weight and drag. With balancing of the fuselage keel area, the tailplane was high-mounted so that the rudder could operate effectively.
To save development time the undercarriage was fixed, with trouser fairings. To reduce drag further, Martin fitted the oil-cooler in the leading edge of the port fairing. A 60 lb/sq.in pneumatic system operated the split flaps and the wheel brakes. There was no hydraulic system.
The aircraft was generously provided with inspection and maintenance access points. The engine complete could be removed and replaced in less than 90 minutes. The complete outer wing assembly could be removed in 25 minutes. The machine-guns, together with their ammunition tanks, were locked in position with pins, removal via a very large access panel taking just five minutes.
The private venture MB.2 prototype was completed in July 1938, the Air Ministry making RAF Harwell available for flight tests. The MB.2 arrived late in the month, painted in a strange "air-force green" livery overall, and sporting the totally unofficial identity 'M-B-1’.
Val Baker first flew this prototype on August 2, 1938, a few days after the sixth production Spitfire had been delivered to the RAF. He found that directional stability was poor. The aircraft was quickly fitted with a vestigial fin, and also at that time, allotted the civil registration G-AEZD. Even with the addition of the miniature fin, Baker found the handling unsatisfactory, though he achieved a level speed of 320mph (515km/h) at a weight of 5,530 lb (2,500kg), which included guns and ammunition.
After initial company tests, the Air Ministry accepted the MB.2 for evaluation purposes, the aircraft being repainted overall deep olive green and allotted the service serial P9594. It arrived at A&AEE, then still at Martlesham Heath, during November 1938. James Martin went with the aircraft and explained to those concerned his thinking behind the configuration.
In the official A&AEE report, which was issued the following month, the MB.2 received high praise as a piece of engineering. As a flying machine it was unpopular. The ease of maintenance and accessibility drew considerable acclaim. The cockpit area attracted mixed comments. It was praised as warm and comfortable, roomy and draught-free, but the unjettisonable canopy was criticised. The wind-down side windows were popular but an openable direct-vision panel ahead was needed. The cockpit was assessed as difficult to enter and an extra step was suggested. However, the excellent view from the cockpit drew favourable comment, as did the crash-pylon.
Flap actuation also attracted criticism; the flaps were operated by a simple lever which provided full-flap for landing, without an intermediate setting, and only a meagre warning light showed when they were down. The A&AEE suggested a more positive flap position indicator, and also different trimming facilities. Armament arrangements were praised; the guns were made accessible through quick-release hatches and working platforms were formed into the wing upper surfaces.
The handling of the MB.2 was unacceptable to the testing authorities. The elevators were over-sensitive, particularly with power off; lower gearing was suggested. Ailerons left much to be desired, being ineffective at low speeds and heavy at high speeds. The rudder layout was found to be particularly poor and produced considerable yaw even with small movements. At high power, even full left rudder could not prevent a gentle turn in the opposite direction. Stability in all three planes was thus found wanting, and consequently the MB.2 made a poor gun platform. Finally it was an uncomfortable ride for the pilot.
After the tests at Martlesham P9594 returned to Denham, where the fin and rudder were modified once more, taking on a larger and more conventional appearance. A study was also carried out to enlarge the tailplane, in order to improve pitch behaviour and encourage gliding properties. The modifications appear to have rectified the stability and control problems, for Val Baker was able in May 1939 to give an inspired demonstration at Heston, which included steep, low-level turns and a dive at some 400mph (644km/h). It seems that the length of the Dagger, which might have reduced power of manoeuvre except in roll, was offset by the comparatively short wing span.
The Air Ministry purchased the only MB.2 built in July 1939 intending to use it as a test-bed, the aircraft eventually returning to Denham where it was dismantled in 1941.
Engine: One 798hp (595kW) Napier Dagger M.3 24 cylinder H--type piston
Max speed 320mph (514km/h)
Normal range 300 miles (482km)
Operational ceiling 31,000ft (9448m)
Empty weight 3,840 lb (1,741kg)
All-up weight 5,400 lb (2,449kg)
Wingspan 34ft (10.3m)
Length 34ft 6in (10.3m)
Height 12ft 3in (3.3m)
Wing area 235sq.ft (21.8sq.m)
Armament: Eight 0.303 in Browning machine guns.