The Grumman F4F Wildcat was conceived around the same time as the Brewster Buffalo, and was a direct competitor for a US Naval order for shipboard fighters. Its short, rotund fuselage was reminiscent of the biplane fighters that preceded it, and it was powered by a fourteen-cylinder two-row Pratt & Whitney R-1830-66 Twin Wasp of 1050 hp. The F4F was of all-metal construction with fabric-covered control surfaces and featured a mid-set wing of NACA 230 series section. The undercarriage retracted into wells in the fuselage to the rear of the engine. The armament initially comprised two fuselage-mounted 0.5-in Browning machine-guns firing through the propeller arc, although provision was also made for two further Browning guns in the wings.
The prototype XF4F-2 was flown for the first time by Robert L. Hall at Bethpage on 2 September 1937. It was delivered to the Anacostia Naval Air Station for trials work and a comparative assessment with the Brewster XF2A-1 and the Seversky HF-1 (a naval adaptation of the P-35). As the maximum speed of the latter was only 250 mph, it was quickly dropped from the competition, leaving the contenders from Grumman and Brewster to fight it out. Although a production contract was awarded to the XF2A-1, the promise shown by the Grumman fighter was sufficient for the drafting of a development contract for a more advanced version. This was the XF4F-3, which was powered by an XR-1830-76 Twin Wasp with a two-stage supercharger offering 1200 hp for take-off and 1000 hp at 19,000 ft. Other modifications included a wing of increased span and area, squared off wing tips and a taller fin. Although the weight had gone up by 600 lb to 5986 lb, the maximum speed was now 334 mph at 20,500 ft.
The first production F4F-3 took to the air in February 1940, and the type was selected by France for use as a shipboard fighter, but with a 1200 hp Wright Cyclone R-1820-G205A-2 with a single-stage, two-speed supercharger. No deliveries had been made by the time of the French collapse and the order was transferred to Britain for the Fleet Air Arm, where the aircraft became known as the Martlet I. The first examples did not feature wing-folding and were armed with four 0.50-in guns in the wings. Subsequent variants were the Martlet II and III, (both powered by a Twin Wasp), the Martlet IV and V (which from January 1944 became known as the Wildcat IV and V) and the Wildcat VI.
Handling trials were carried out at A&AEE Boscombe Down using Martlet I AX826. The cockpit could be entered from either side of the aircraft, as a foothold and handhold were provided on each side of the fuselage, together with a ‘non-slip’ coating on the wing root. Having climbed up the wing, access to the cockpit was rather awkward, and another handhold at the top of the windscreen would have been a big improvement. The pilot’s seat was relatively comfortable and could be adjusted for height by releasing a catch on the right-hand side of the seat. However the counter balance arrangement proved to be insufficiently strong, and to raise the seat the pilot had to take his feet off the rudder pedals and press on the floor. Even so, a further 1–2 in of upward movement was really needed to provide the best possible view around the nose for landing.
At cruising rpm the cockpit was quieter than most other fighters of the period, and the noise did not become excessive at any time. Although no heating was provided, the cockpit did not get particularly cold, but after flying for a considerable period with the hood closed, pilots became aware of a distinct smell of engine fumes. This posed something of a dilemma, as on opening the hood to disperse the fumes, the pilot was hit by almost unbearable draught, which buffeted the head quite violently, except when flying at very low rpm. The hood was not particularly easy to move and both hands were required to slide it backwards or forwards. More marks were lost by the American-type oxygen equipment, which was considered unsatisfactory as there was no indication of the rate of flow or any warning should the supply fail. As a result of the severe draughts experienced at high power settings, most pilots elected to take-off with the hood closed.
The view from the cockpit was good at all times, especially to the rear. There was no clear view panel fitted, but this was not missed during the approach, as the hood could be opened without too much discomfort when the engine was throttled back. A clear view panel would have been of use, however, during longer flights in bad weather. On a number of occasions, the windscreen iced up badly when descending from high altitude. As there was no cockpit heating, this took some time to clear at low level, an aspect of the Martlet that would be of obvious concern to pilots returning low on fuel.
On the ground, all the control surfaces could be moved without excessive friction or play. The control column had a solid vertical handgrip incorporating a gun-firing trigger and bomb release. For ease of use, it was felt that it needed to be slightly longer and a little nearer the pilot. The rudder pedals were of the pendulum type and could be adjusted fore-and-aft. Trim tabs were provided for the elevator, rudder and port aileron, and the controls were mounted on the left-hand side of the cockpit near the pilot’s forearm. Indicators were provided for all three. The controls were easy and smooth to operate, and showed no tendency to slip. In flight, however, the trimmer controls iced up on several occasions, and attempts to free them resulted in failures.
The throttle and mixture controls were located in a quadrant on the left-hand side of the cockpit, and fell nicely to hand. Once again, there was no automatic boost, the throttle having to be readjusted after every change in height or speed, particularly in a dive when boost would quickly rise above limiting values if not constantly watched. A gate was provided on the throttle at the position for maximum take-off boost. The mixture control lever could be moved to any one of four positions – fully rich, automatic rich, automatic weak or idle cut-out – and the control for the constant-speed propeller consisted of a ‘push-pull’ knob at the bottom left-hand side of the panel. The fuel cock was positioned behind the throttle and elevator trimmer.
Other major controls included the supercharger gear change, consisting of a ‘push-pull’ handle on the bottom right-hand side of the panel, and the emergency hand-operated fuel pump and ignition switches on the opposite side. The flap control was also on the left of the cockpit behind the rudder trimmer. As it was of similar shape to the fuel cock handle located nearby, there was a distinct possibility that a pilot would operate the wrong one if distracted, or when flying at night. The undercarriage was retracted by a manual crank handle near the pilot’s right knee and a safety catch had to be moved before it could be turned. For a manual system the operation was relatively easy, and the wheels could be retracted in 25–30 seconds. If the engine was throttled back with the undercarriage up: a red light appeared on the left of the panel and a horn sounded. A lever to lock the tailwheel was located just forward of the throttle quadrant.
The brakes were operated via toe pedals and were not particularly efficient, being too stiff and insensitive in operation. Each wheel had its own independent system and so it was difficult to apply equal pressure to each side when pulling up from a straight run. The instruments were generally well positioned, except for the engine speed indicator, which was positioned at the extreme right-hand side of the panel. No heating was provided for the pitot head.
Taxying was relatively straightforward and the view on the ground was good. Owing to the narrowness of the undercarriage, however, there was a tendency for one leg to compress more than the other, and the aircraft tended to list considerably in a strong crosswind. It was also difficult to turn against a strong wind. Before attempting to takeoff, the tailwheel lock had to be engaged and the aircraft taxied a short distance to ensure that the lock had taken effect. Take-offs were normally made with the flaps up, but with full right rudder trim (three divisions) and about half a division of nose-down elevator trim. Despite the application of full right rudder trim, there was still a tendency to swing to the left and further right rudder was required. The tailwheel did not come up particularly quickly during the early part of the take-off, but the aircraft left the ground at 82 mph IAS after a relatively short run. It was recommended that the undercarriage be raised immediately the aircraft became airborne, and some trimming was required to remove the slight tail heaviness produced.
Once in the climb, the aircraft could be trimmed to fly ‘hands and feet off’. In all manoeuvres, the controls were light and effective, particularly the ailerons. The lightness of the aileron control was consistent throughout the speed range, but the rudder and elevators tended to become heavier with increases in speed. Response to all controls was excellent and aileron trim was regarded as superfluous.
Stability checks were made using Martlet I AX828 with a normal CG loading. Although it was stable in level flight, it showed signs of instability on the climb with the flaps and undercarriage up. As CG was moved further back, the aircraft became increasingly unstable longitudinally in the climb, when cruising, in full throttle level flight and in the glide (flaps and undercarriage up). Any displacement of the control column produced a divergence, which at extended aft CG would normally have been regarded as unacceptable. As the initial stages of the divergence were not vicious, however, and in view of the generally good flying qualities of the aircraft and its operational duties, it was felt that the aircraft could be cleared at this CG position. When CG was moved forward, the aircraft’s longitudinal stability became practically neutral. Following any disturbance from a trimmed condition, it tended to remain in its disturbed position, the speed only changing very slowly back to its original value.
Stall speeds were found to be 83 mph IAS with the flaps and undercarriage up and 70 mph IAS with the flaps and undercarriage down. When gliding at 1.2 × stall speed in the clean configuration, the aircraft was pleasantly stable, the control column having to be brought back about one-third of its total travel in order to produce a stall. Very little stick force was needed to do this, and the only warning of the approaching stall was a slight shake of the control column and the high position of the nose. With the flaps and undercarriage down, it was impossible to trim the aircraft to glide at 1.2 × stall speed, unless the airscrew was fully coarse. The control column had to be brought back four-fifths of its travel and the nose was very high at the stall.
A comfortable approach could be made using full flap at about 90 mph IAS with 1600 rpm set. Most pilots elected to open the hood prior to landing to obtain a good view of the landing area, but it was imperative to wear goggles when leaning over the side because of the violence of the slipstream. To minimise the risk of swinging on landing, it was best to adopt a three-point attitude on touchdown and to apply the brakes carefully and evenly. Any tendency to swing in the latter stages of the landing run had to be checked immediately. There was no tendency to nose-over on braking, even with CG in the extended forward position.
The first Martlet Is entered service with No. 804 Squadron at Hatston on 8 September 1940 and a total of ninety-one ex-French aircraft were delivered. The next in line was the Martlet II, which differed from its predecessor in having a Twin Wasp S4C4-G engine, folding wings and six 0.5-in wing-mounted machine-guns instead of four. Handling trials were carried out at Boscombe Down in early 1942 using AM969. Many of the unsatisfactory aspects of the Martlet I cockpit were still present, although a control was now provided to supply heated air to the windscreen and a rear-view mirror had been positioned in the roof above the pilot. The view over the nose, both on the ground and in the air, was an improvement on the previous aircraft due to the revised shape of the engine cowling. However, problems were still experienced when flying with the hood open. On this occasion a shrill screaming noise that was painful to the ears was experienced when the hood was moved to the two-thirds open position.
Unlike the Martlet I, the controls could be locked on the ground by a cap, which fitted over the control column with wires extending to the rudder pedals and to each side of the bulkhead behind the pilot’s seat. The trimming controls were as before, except that one more division of right rudder trim was available to counter the swing on take-off. The controls for the Curtiss Electric propeller, consisting of a master switch, four-position selector switch and push-pull control knob, were grouped together at the bottom left-hand side of the panel. When the selector switch was set to ‘automatic’, the control knob increased propeller speed when it was pushed and vice versa. When set to ‘manual’, the control knob became inoperative and the propeller speed could be changed by moving the switch to the left or right, and holding it there until the desired rpm was reached. The supercharger gear change control was located on the lower left-hand side of the panel (instead of the right as on the Martlet I). The flap control lever had been moved forward of the aileron trimmer to avoid any confusion with the fuel cock handle. The instruments were the same as on the Martlet I, except that there was now provision for heating the pitot head.
In case of emergency, the hood could be jettisoned by pulling on two red rings at the forward end of the hood on each side. It was considered that it would be extremely difficult to open the hood if the aircraft was inverted on the ground, even from the outside. However, as it was relatively fragile, it should have been easy to break to allow a pilot to escape. The bulkhead behind the pilot appeared to be substantial enough to take the weight of the aircraft when inverted.
On take-off, the tendency to swing to the left was even more pronounced, but this could be anticipated with the extra rudder trim that was available. The controls were not quite as good, the ailerons in particular being noticeably heavier, but they were still pleasant to operate. The landing characteristics were the same as on the Martlet I.
Performance testing took place at A&AEE in April 1942 using AM991 at a take-off weight of 7790 lb. The testing showed a maximum rate of climb of 1940 ft/min at 7600 ft in MS gear and 1570 ft/min at 13,700 ft in FS gear. Compared with most land-based fighters, the climb performance of the Martlet II was relatively sedate, taking 5.3 minutes to reach 10,000 ft and 12.5 minutes to reach 20,000 ft. For its naval role this was considered acceptable, but its climb rate deteriorated rather dramatically above this height, the aircraft taking a full 30.6 minutes to get to 30,000 ft. Its service ceiling (100 ft/min climb rate) was estimated at 31,000 ft. Level speed tests showed a maximum of 293 mph TAS at 5400 ft in MS gear, with an identical speed at 13,800 ft in FS gear. The recommended height to change supercharger gear was around 11,500 ft.
Only ninety Martlet IIs were delivered, although some of these ended up at the bottom of the sea en route to the Far East. The Martlet III was also powered by a Twin Wasp, but was delivered in even smaller numbers, ten arriving under British contract and thirty from a defunct Greek order. The first variant to be flown by the FAA in any great number was the Martlet IV, which reverted to the Wright Cyclone engine (unlike its US Navy equivalent which retained a Twin Wasp). A total of 220 were delivered.
In September 1942 handling trials at aft CG took place at Boscombe Down using Martlet IV FN111 at an all-up weight of 7750 lb. Unlike the previous variants, exhaust fumes did not appear to seep into the cockpit, and the aircraft could be flown with the hood closed when required without danger of contamination. The cockpit controls were virtually identical to the Martlet I, except that cowling gills were fitted. These were adjusted by a small cranked handle on the right of the panel (as in the Martlet II).
The flying controls were tested in a series of high-speed dives. Although they became progressively heavier with increases in speed, they remained relatively light and pleasant to use up to about 350 mph IAS. Above 400 mph IAS, however, the ailerons were almost immovable and the rudder was extremely heavy. Three dives were made to a speed of 410 mph IAS, with the aircraft trimmed for all-out level flight. During these dives the aircraft became uncomfortably nose-heavy. As a result, a considerable pull force had to be exerted on the control column and much height was needed to effect recovery. It also showed a tendency to yaw to the right, but this could be held with rudder, even though it was not possible to yaw the aircraft more than three degrees
A fourth dive was made to 460 mph IAS. However, in view of the large pull force previously required, the dive was entered with the elevator trimmer set to zero, a slightly more nose-up setting from that previously used. With this setting, tail heaviness was maintained throughout the dive. As soon as recovery was initiated, with not more than 4 g being imposed, the top surface of the inboard end of the starboard folding wing lifted approximately half an inch clear of the upper surface of the centre section. This was not considered serious and was because the top surface of the folding wing was spring-loaded at the inboard end.
With CG in the rearmost position, the aircraft was markedly unstable longitudinally on the climb and slightly less so during level flight. With the flaps and undercarriage up, it was unstable on the glide to the extent that if it was disturbed from its trimmed state and the control column left free, the amplitude of the resultant oscillation would increase to the point where the aircraft stalled. On the glide with the flaps and undercarriage down, longitudinal stability became neutral. Directionally and laterally, the Martlet IV was stable under all conditions of flight.
Trials to assess the climb rate and maximum level speed were also made using FN111, which although capable of carrying two 100-lb bombs under the wings, did not have racks fitted. Take-off weight was 7740 lb. Its performance proved to be somewhat worse than the Martlet II, with a maximum rate of climb of 1580 ft/min at 6200 ft in MS gear and 1440 ft/min at 14,600 ft in FS gear. The times to height were: 10,000 ft – 6.6 minutes; 20,000 ft – 14.6 minutes; 28,000 ft –29.1 minutes. The estimated service ceiling was 30,100 ft. The maximum speed in MS gear was 278 mph TAS at 3400 ft and 298 mph TAS at 21,000 ft in FS gear.
The Martlet IV was followed by the Martlet V, which was the British equivalent of the US Navy’s FM-1. The new designation denoted that the aircraft was built by the Eastern Aircraft Division of General Motors instead of Grumman. Total deliveries amounted to 312 aircraft. The final variant was known from the outset as the Wildcat VI (US Navy FM-2). It was aerodynamically similar to the previous machines, except for increased fin and rudder area to counteract take-off swing accentuated by the use of a more powerful Cyclone R-1820-56 engine of 1350 hp. The Wildcat VI was the most numerous of the Martlet/Wildcat variants in FAA service, with 340 being delivered.
Handling and performance trials involving JV642 took place at Boscombe Down in April 1944. The taller fin and rudder proved to be a big improvement and provided sufficient directional control to enable full flap take-offs to be made with ease. Directional stability on glides was also much better. The latest version of the Cyclone engine not only produced more power, but also weighed less as forged cylinder heads were used. JV642 weighed in at 7100 lb. As a result, performance was improved, with a maximum level speed of 307 mph TAS at 3400 ft in MS gear and 322 mph TAS at 16,800 ft in FS gear. The performance on some late production examples of the Wildcat VI was improved still further by the use of Cyclone engines with water-injection, designated R-1820-56W. Trials with JV782 showed an increase in the top speed of 13 mph TAS at all heights up to 9300 ft, as a result of the increased manifold pressure available when using water-injection.
The Martlet/Wildcat had the distinction of serving with the FAA from the beginning of the war to the very end. An early success was achieved by two Martlet Is of No. 804 Squadron when a Junkers Ju 88 attacking the Home Fleet at Scapa Flow was forced down on 25 December 1940. This was the first German aircraft to be lost to American aircraft in British service. With the arrival of the Martlet II with folding wings, the type was taken to the seas, mainly on light escort carriers. Its duties included protecting convoys from attacks by long-range Focke-Wulf Fw 200 maritime reconnaissance bombers, and acting as fighter cover for strikes by Swordfish torpedo-bombers. Martlets also took part in cover operations during the Allied invasion of North Africa in November 1942 and the Salerno landings in the Mediterranean in September 1943. With the delivery of the Wildcat VI, commencing in July 1944, the FAA maintained its connection with the Grumman fighter and this variant was used mainly in the Far East. The culmination of a remarkably long career in FAA service was the shooting down of four Bf 109s on 26 March 1945 by Wildcats of No. 882 Squadron during a fighter sweep over Norway.