Gloster Gladiator

The Gloster Gladiator is a British biplane fighter. It was used by the Royal Air Force (RAF) and the Fleet Air Arm (FAA) (as the Sea Gladiator variant) and was exported to a number of other air forces during the late 1930s.

Developed privately as the Gloster SS.37, it was the RAF's last biplane fighter aircraft, and was rendered obsolescent by newer monoplane designs even as it was being introduced. Though often pitted against more advanced fighters during the early days of the Second World War, it acquitted itself reasonably well in combat.

The Gladiator saw action in almost all theatres during the Second World War, with a large number of air forces, some of them on the Axis side. The RAF used it in France, Norway, Greece, the defence of Malta, the Middle East, and the brief Anglo-Iraqi War (during which the Royal Iraqi Air Force was similarly equipped). Other countries deploying the Gladiator included China against Japan, beginning in 1938; Finland (along with Swedish volunteers) against the Soviet Union in the Winter War and the Continuation War; Sweden as a neutral noncombatant (although Swedish volunteers fought for Finland against the USSR); and Norway, Belgium, and Greece resisting Axis invasion of their respective lands.

South African pilot Marmaduke "Pat" Pattle was the top Gladiator ace with 15 victories with the type.Mason 1966, p. 10.

Design and development

Origins

During the 1920s, Britain's air defences had been based around interceptor aircraft capable of flying only for short ranges and at speeds of , but by 1930, figures within the Air Ministry were keen to supersede these aircraft. In particular, some dissatisfaction had arisen with the level of reliability experienced with the 'one pilot, two machine guns' design formula previously used; the guns were often prone to jams and being unreliable.Mason 1966, p. 3. The Air Ministry's technical planning committee formulated Specification F.7/30, which sought a new aircraft capable of a maximum speed of at least , an armament of no fewer than four machine guns, and such handling that that same fighter could be used by both day and night squadrons. Gloster, being already engaged with development of the Gloster Gauntlet, did not initially respond to the specification, which later proved to be beneficial.Mason 1966, pp. 3-4.

The specification had also encouraged the use of the new Rolls-Royce Goshawk evaporatively cooled inline engine; many of the submissions produced by various aviation companies in response accordingly featured the Goshawk engine.Mason 1966, p. 4. However, the Goshawk engine proved to be unreliable, mainly due to its overcomplex and underdeveloped cooling system, and unsuited to use on fighter aircraft and this outcome stalled development of the aircraft intended to use it. A further stumbling point for many of the submitted designs was the placement of the machine gun breeches within arm's reach of the pilot. At the same time, the development of monoplane fighters such as the Hawker Hurricane and Supermarine Spitfire cast doubt over the future viability of the requirement altogether.

Gloster recognised that instead of developing an all-new design from scratch, the existing Gauntlet fighter could be used as a basis for a contender to meet Specification F.7/30. Development of what would become the Gladiator began as a private venture, internally designated as the SS.37, at Gloster, by a design team headed by H.P. Folland, who soon identified various changes to increase the aircraft's suitability to conform with the demands of the specification. Making use of wing-design techniques developed by Hawker Aircraft, the new fighter adopted single-bay wings in place of the two-bay wings of the Gauntlet, and two pairs of interplane struts were also dispensed with as a drag-reduction measure. The Bristol Mercury M.E.30 radial engine, capable of generating , was selected to power the SS.37, which provided a performance boost over the preceding Gauntlet. Another design choice was the fitting of a cantilever main undercarriage, which incorporated Dowty internally sprung wheels, allowing for more simple rigid landing gear struts.Lumsden 1992, p.10.James 1971, p. 206.

Prototype

In spring 1934, Gloster embarked on the construction of a single SS.37 prototype. On 12 September 1934, the SS.37 prototype conducted its maiden flight, piloted by Gloster chief test pilot Gerry Sayer. Initially powered by a Mercury IV engine, the prototype was quickly re-equipped with a more powerful Mercury VIS engine. During flight tests, the prototype attained a top speed of while carrying the required four machine guns (two synchronised Vickers guns in the fuselage and two Lewis guns under the lower wing). According to aviation author Francis K. Mason, the Air Ministry were sceptical about the aircraft achieving such performance from a radial engine design, so funded a protracted series of evaluation trials.

On 3 April 1935, the prototype was transferred to the RAF, receiving the designation ''K5200'', and commenced operational evaluations of the type. Around the same time, Gloster proceeded to plan a further improved version, featuring an Mercury IX engine, a two-blade wooden fixed-pitch propeller, improved wheel discs, and a fully enclosed cockpit.James 1971, pp. 206–207. ''K5200'' was later used to trial modifications for production aircraft, such as the addition of a sliding hood for the pilot.

In June 1935, production plans for the aircraft were proposed; two weeks later, a production specification, Specification F.14/35, had been rapidly drawn up, partially prompted by events in continental Europe, such as the invasion of Abyssinia by Fascist Italy and the rise of Adolf Hitler to power in Germany, in response to which the British government mandated an urgent expansion of the RAF to counter the emerging threats. This culminated in an initial order for 23 aircraft. On 1 July 1935, the aircraft formally received the name ''Gladiator''.Lumsden 1992, p. 12.

Production

Manufacturing of the Gladiator was started at Gloster's Hucclecote facility. Production of the initial batch was performed simultaneously, leading to many aircraft being completed around the same time. On 16 February 1937, ''K6129'', the first production Gladiator, was formally accepted by the RAF; on 4 March 1937, ''K6151'', the last aircraft of the initial batch, was delivered. In September 1935, a follow-up order of 180 aircraft was also received from the Air Ministry;James 1971, p. 207. this order had the proviso that all aircraft had to be delivered before the end of 1937.

Variants

The first version, the Gladiator Mk I, was delivered from July 1936, becoming operational in January 1937. When difficulties with Rolls-Royce Merlin combustion chamber threatened to postpone the readiness of the next-generation fighters, the Air Ministry hedged its bets by procuring three hundreds of Mk II Gladiators as a stopgap