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Westland Whirlwind

The Westland Whirlwind was a twin-engined heavy fighter of British origin.

It was contemporaneous with the Supermarine Spitfire and Hawker Hurricane, and was the first single-seat, twin-engined, cannon-armed fighter of the Royal Air Force.

Upon its maiden flight in 1938, the Whirlwind was among the fastest combat aircraft in the world and boasted the most substantial armament with four 20 mm Hispano-Suiza HS.404 autocannon in its nose.

However, the project was plagued by prolonged development issues with its Rolls-Royce Peregrine engines, resulting in the production of only 114 Whirlwinds.

Despite its success as a fighter and ground attack aircraft during the Second World War, only three RAF squadrons were equipped with the aircraft, and it was ultimately withdrawn from service in 1943.

In the mid-1930s, aircraft designers worldwide recognized that increased attack speeds were resulting in shorter firing times for fighter pilots.

This led to less ammunition hitting the target and ensuring destruction.

As a result, six or eight machine guns were required instead of two rifle-calibre machine guns.

Studies had shown that eight machine guns could deliver 256 rounds per second.

However, the rifle-calibre rounds fired by the eight machine guns installed in the Hurricane did not deliver enough damage to quickly knock out an opponent, and were dispersed at ranges other than that at which they were harmonised.

Therefore, cannon, such as the French 20 mm Hispano-Suiza HS.404, which could fire explosive ammunition, offered more firepower.

Attention turned to aircraft designs that could carry four cannon.

Although the most agile fighter aircraft were generally small and light, their meagre fuel capacity limited their range and tended to restrict them to defensive and interception roles.

The larger airframes and bigger fuel loads of twin-engined designs were favoured for long-range, offensive roles.

The first British specification for a high-performance machine-gun monoplane was Air Ministry specification F.5/34 for a radial-engined fighter for use in the tropics.

This led to four aircraft designs, but the aircraft produced were overtaken by the development of the new Hawker and Supermarine fighters.

The RAF Air Staff believed that an experimental aircraft armed with the 20 mm cannon was urgently needed, and specification F.37/35 was issued to British aircraft companies in 1935.

The specification called for a single-seat day and night fighter armed with four cannon.

The top speed had to be at least 40 mph (64 km/h) greater than that of contemporary bombers – at least 330 mph (530 km/h) at 15,000 ft (4,600 m).

Eight aircraft designs from five companies were submitted in response to the specification.

When the designs were considered in May 1936, there was concern that a two-engine design would be less manoeuvrable than a single-engined design, and that uneven recoil from cannon set in the wings would give less accurate fire.

The conference favoured two engines with the cannon set in the nose and recommended the Supermarine 313.

However, neither Supermarine nor Hawker were in a position to deliver a modified version of their single-engined designs quickly enough.

Westland, which had less work and was further advanced in their project, was chosen along with the P.88 and the Type 313 for construction.

The Westland design team, under the new leadership of W. E. W. “Teddy” Petter, designed an aircraft that employed state-of-the-art technology.

The monocoque fuselage was tubular, with a T-tail at the end.

The engines were developments of the Rolls-Royce Kestrel K.26, later renamed Peregrine.

The airframe was built mainly of stressed-skin duralumin, with the exception of the rear-fuselage, which used a magnesium alloy stressed skin.

Four 20 mm cannon were mounted in the nose, making it the most heavily armed fighter aircraft of its era.

The Whirlwind exhibited excellent handling characteristics and proved to be very easy to fly at all speeds.

However, it had short range, under 300 mi (480 km) combat radius, which made it as marginal as an escort as the Hurricane and Spitfire.

By late 1940, the Spitfire was scheduled to mount 20 mm (0.79 in) cannon, so the “cannon-armed” requirement was being met.

The main qualities the RAF were looking for in a twin-engine fighter were range and carrying capacity, in which requirements the Bristol Beaufighter could perform just as well as or even better than the Whirlwind.

Despite the Whirlwind’s promise, production ended in January 1942, after the completion of just 112 production aircraft (plus the two prototypes).

Rolls-Royce needed to concentrate on the development and production of the Merlin engine, and the troubled Vulture engines, rather than the Peregrine.

Westland was aware that its design – which had been built around the Peregrine – was incapable of using anything larger without an extensive redesign.

After the cancellation of the Whirlwind, Petter campaigned for the development of a Whirlwind Mk II, which was to have been powered by an improved 1,010 hp (750 kW) Peregrine, with a better, higher-altitude supercharger, also using 100 octane fuel, with an increased boost rating.

This proposal was aborted when Rolls-Royce cancelled work on the Peregrine.


P.9 prototype

Single-seat twin-engine fighter aircraft prototype

Two built (L6844 and L6845), can be distinguished from later production samples by the mudguards above the wheels (Though the first production sample (P6966) had them as well), the exhaust system and the so-called ‘acorn’ on the joint between fin and rudder.

L6844 had a distinctive downward kink to the front of its pitot tube, atop the tail not seen again in following models.

L6844’s colour was dark grey. L6844 had opposite-rotation engines, L6845 had the same rotation engines as per production machines.

Whirlwind I

Single-seat twin-engine fighter aircraft, 400 ordered, 2 prototype & 114 production aircraft, total aircraft built 116

Whirlwind II

Single-seat twin-engine fighter-bomber aircraft, fitted with underwing bomb racks, were nicknamed “Whirlibombers”.

At least 67 conversions made from the original Mk I fighter.

Experimental variants A Mk I Whirlwind was tested as a night fighter in 1940 with No. 25 Squadron.

The first prototype was armed with an experimental twelve 0.303 machine guns and another one 37 mm cannon.

Merlin variant Westland proposed fitting Merlin engines in a letter to Air Marshal Sholto Douglas.

The proposal was rejected but Westland used the design work already performed in developing the Welkin high-altitude fighter.





32 ft 3 in (9.83 m)


45 ft 0 in (13.72 m)


11 ft 0 in (3.35 m)

Wing area

250 sq ft (23 m2)



NACA 23017


NACA 23008

Empty weight

8,310 lb (3,769 kg)

Gross weight

10,356 lb (4,697 kg)

Max take-off weight

11,445 lb (5,191 kg)


2 × Rolls-Royce Peregrine I V-12 liquid-cooled piston engines, 885 hp (660 kW) each at 10,000 ft (3,000 m) with 100 octane fuel


3-bladed de Havilland-Hydromatic, 10 ft (3.0 m) diameter variable-pitch propellers


Maximum speed

360 mph (580 km/h, 310 kn) at 15,000 ft (4,600 m)

Stall speed

95 mph (153 km/h, 83 kn) flaps down


800 mi (1,300 km, 700 nmi)

Combat range

150 mi (240 km, 130 nmi) as low altitude fighter, with normal reserves

Service ceiling

30,300 ft (9,200 m)

Time to altitude

15,000 ft (4,600 m) in 5 minutes 54 seconds, 30,000 ft (9,100 m) in 20 minutes 30 seconds



4 × Hispano 20 mm cannon with 60 rounds per gun


Options of 2 × 250 lb (115 kg) or 500 lb (230 kg) bombs.

Westland Aircraft Since 1915-Derek N. James.
The Book of Westland Aircraft-A H Lukins.
Westland, Plane Makers 2-David Mondey.
Whirlwind, The Westland Whirlwind Fighter-Victor F. Bingham.
Westland Whirlwind Described-Bruce Robertson.
Westland Whirlwind-Michal Ovčáčík & Karel Susa.
Westland Whirlwind-Profile Publications 191.



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