Classic British fighters – The Sopwith Pup

The Sopwith Pup

The Sopwith Pup was a single-seat biplane fighter built by the Sopwith Aviation Company, and was arguably the first ‘true’ British fighter when it entered service with the Royal Flying Corps and the Royal Naval Air Service in the autumn of 1916. Armed with a single fixed forward-firing machine gun, synchronised to fire through the propeller disc, the Pup possessed very pleasant flying characteristics without any vices, excellent agility in the air and adequate performance, and proved very successful.

Genesis
In February 1916 the Sopwith company’s experimental department passed the prototype of a single-seat ‘fighting scout’ designed by Herbert Smith, whose 1½-Strutter two-seat warplane was currently in production. The new single-seater bore a distinct family resemblance to the 1½-Strutter even though it was somewhat smaller in overall dimensions and powered by an air-cooled rotary engine developing only 80 hp (59.6 kW). As such, the new warplane was essentially a military development of the little single-seater that had been built in 1915 as a personal transport and aerobatic aircraft for Sopwith’s test pilot, Harry Hawker. A single-seat tractor biplane powered by a 50-hp (37.3-kW) Gnome air-cooled seven-cylinder rotary engine, this became known as Hawker’s Runabout, and another four similar aircraft have been tentatively identified as Sparrow aircraft. Sopwith next developed a larger fighter that was heavily influenced by this design, though more powerful and controlled laterally with ailerons rather than by wing warping. To the flying services to which it was delivered the new ‘fighting scout’, as the fighters of the period were called, was so manifestly the descendant of the 1½-Strutter that it was unofficially named the Pup, and despite all protestations from service departments that disliked so familiar a name and therefore allocated more bureaucratic titles, the name has been used ever since.

First production
During 1916 Sopwith was primarily a contractor to the Admiralty, and the first Pup fighters were therefore delivered to the Royal Naval Air Service, which was the flying service of the Royal Navy. The first prototype was followed by five more prototypes: it is no longer known what type of engine was installed in the first machine, but the following five aircraft were each fitted with a Clerget air-cooled rotary engine rated at 80 hp (59.6 kW). One of the six prototypes was allocated to the ‘A’ Squadron based at Furnes in May 1916, and the naval pilots immediately reported favourably on the fighter’s combination of excellent performance despite the availability of only 80 hp (59.6 kW) and beautiful handling characteristics.

The Admiralty contracted with the Sopwith company and with William Beardmore & Co., and in the practice of the period used the serial number of the first Beardmore-built Pup as the official designation for the new fighter, which was therefore known formally as the Type 9901. Like the prototypes, the first 11 Pup aircraft of the first Beardmore batch had the Clerget engine rated at 80 hp (59.6 kW), but all the remainder had the Le Rhône 9C air-cooled nine-cylinder rotary engine, which was also rated at 80 hp (59.6 kW) and became the engine that was generally used in the Pup.

Description
The aeroplane was a type of great and indeed elegant simplicity in its overall appearance and in its construction. The aeroplane was an equal-span biplane of wooden construction covered mainly with fabric except on the forward fuselage that was skinned with light alloy, and its structural core was the fuselage. This was of rectangular section with a rounded upper decking covered with plywood, an essentially straight upper line and a curved lower line. In structural terms the fuselage was of the type standard in this period, namely an internally wire-braced wooden box girder unit with four longerons and a number of horizontal and vertical spacers. From front to rear, this fuselage carried the powerplant, fuel and oil tanks, pilot’s open cockpit, and tail unit. The tail unit comprised single horizontal and vertical surfaces, the former including a wire-braced tailplane of wooden construction carrying plain elevators of steel tube construction, and the latter comprising a wire-braced steel tube fin carrying a plain rudder of steel tube construction and hinged at its lower end to the vertical knife-edge in which the fuselage ended.

The staggered wing cellule was based on wooden wings that were to all practical purposes identical in planform with constant thickness and chord to their inversely raked tips; wire-connected ailerons, of steel tube construction, were fitted on the outboard ends of both the upper and lower wings’ trailing edges. The dihedralled halves of the lower wing extended from the lower longerons, while the dihedralled outer panels of the upper wing extended from a flat centre that incorporated a cut-out in the trailing edge over the pilot’s cockpit and, in some aircraft, a clear-glazed section in its centre to improve the pilot’s upward field of vision: this centre section was supported over the fuselage by two wire-braced sets of outward-canted cabane struts. The upper and lower wings were separated on each side by a single set of parallel interplane struts, and the whole wing cellule was braced with the normal arrangement of flying and landing wires.

The airframe proper was completed by its landing gear, which was of the fixed tailskid type with a main unit of the through-axle type based on a two-wheel axle bungee-bound to the closed ends of two wire-braced V-type struts extending downward and outward from the lower longerons. As noted above, the powerplant was based on either of two types of rotary engine rated at 80 hp (59.6 kW): this engine was installed at the front of the fuselage in an open-fronted circular cowling of light alloy construction, and drove a two-blade wooden propeller of the tractor type.

The armament installed in most Pup fighters was one 0.303-in (7.7-mm) Vickers fixed forward-firing machine gun located centrally on top of the fuselage immediately ahead of the cockpit, and a padded windscreen was attached to the rear of the gun by four short stays. Some operational pilots preferred to discard this windscreen altogether and padded the rear end of the gun for facial protection, and other pilots preferred a wide windscreen at the front of the cockpit opening. On the first Pup fighters of the production line the machine gun was synchronised by means of the Sopwith-Kauper gear, and was fired by the depression of a short lever extending horizontally to the rear from the underside of the section of the gun inside the cockpit, but on later aircraft the Scarff-Dibovski or Constantinesco C.C. synchronising mechanisms, with trigger actuation on the control column, became standard. The Admiralty also specified eight Le Prieur rockets as an alternative to the Vickers machine gun for improved capability against high-value targets such as tethered observation balloons, but in some instances the Pup had both gun and rockets. It is doubtful whether the rocket-equipped Pups saw much operational use.

Into service
The first Pup fighters off the full production line were delivered to No. 2 Squadron of the RNAS and the Dover Defence Flight during October 1916, and by the end of the month 10 aircraft had been delivered. The first Beardmore-built Pup recorded its maiden flight in the last week of September, and deliveries continued until the end of June 1917, when the RNAS accepted its last Beardmore-built Pup. The Pup was also ordered from the Standard Motor Co. Ltd and Whitehead Aircraft Ltd, machines from these two sources being delivered from December 1916 and January 1917 respectively to the Royal Flying Corps rather than the RNAS. The first Standard-built Pup was transferred to the RNAS, however, and while a machine of No. 8 (Naval) Squadron was captured intact by the Germans in January 1917: Germany subjected the aeroplane to an exhaustive evaluation, and this gave the Germans a good indication of what they might expect from the new British fighter.

The Pups of No. 1 (Naval) Wing at Dunkerque were soon successful, for in company with the wing’s Nieuport fighters they downed eight German aircraft in a four-week period in September and October 1916. There was a more pressing demand for the capabilities of the Pup to the south of the coastal region that was the primary operating region for the RNAS’s land-based fighter squadrons. In this more southern area the bitter struggle on the Somme that had begun in July 1916 was dragging on into the autumn, and the RFC was finding itself in difficulty against a renascent German fighter capability. Admittedly, three new squadrons had arrived from England, but of these No. 19 Squadron was equipped with the Royal Aircraft Factory B.E.12, which proved to be virtually useless. Of the five squadrons brought into the Somme area from the north, moreover, two had been transferred elsewhere by October; and all the remaining units had suffered many casualties. In the middle of October, therefore, it was agreed that an RNAS squadron should be formed from the RNAS squadrons in the Dunkerque area for service in the Somme region as assistance for the RFC. The result was No. 8 (Naval) Squadron, or ‘Naval Eight’ as it came to be called. The personnel arrived at Vert Galand aerodrome within days of the decision to create the unit, the squadron’s first aircraft had arrived by the end of October, and the first patrol was flown in the first week of November. The squadron’s initial organisation comprised three flights equipped with Nieuport, 1½-Strutter and Pup fighters.

‘Naval Eight’ soon proved the Pup to be ideal fighting aeroplane, and demanded more of the type. Thus the Pup wholly replaced the 1½-Strutter in the middle of November and the Nieuport machines by the end of the year. This was something of an achievement by Wing Captain C. L. Lambe, currently possessing overall responsibility for the Dover and Dunkerque group of naval air stations. Lambe had to provide the 80-hp (59.6-kW) Le Rhône engines required by the Pups: some came from crashed Nieuport machines while others were begged from the French naval air service, and all were overhauled at Dunkerque and sent to Dover to be installed in the Pup airframes. In November and December 1916 the Pups of ‘Naval Eight’ shot down 20 German aircraft, three of them falling to Flight Sub-Lieutenant D. M. B. Galbraith. The unit was finally withdrawn at the end of January 1917 for re-equipment with the new Sopwith Triplane fighter.

Other Pup, or more formally Sopwith Scout, squadrons were operational or on the verge of becoming so by that time, and No. 54 Squadron of the RFC had reached France on Christmas Eve 1916, No. 3 (Naval) Squadron replaced ‘Naval Eight’ on the first day of February 1917, early in March 1917 No. 66 Squadron of the RFC arrived for service over the Western Front, and in April No. 46 Squadron of the RFC replaced its Nieuport two-seaters with Pups. During various periods of 1917 the Pup was also operated by Nos 2, 4, 9, 11 and 12 (Naval) Squadrons.

Successful fighter
For all that it was lightly built, as part of a successful attempt to improve agility with a low-powered engine through the evolution of an aeroplane with a good power/weight ratio, the Pup proved itself to be a highly capable fighter during the early months of 1917, as shown by the fact that during a single patrol in April 1917 Flight Sub-Lieutenant J. S. T. Fall of No. 3 (Naval) Squadron shot down one Halberstadt and two Albatros single-seat fighters. In another episode, seven Pup fighters of No. 4 (Naval) Squadron, whose primary duties were the provision of offensive patrols and escorts for RNAS aircraft operating from Dunkerque, met a group of Albatros single-seat fighters near Zeebrugge in the middle of May and and shot down no fewer than five of them.

The Pup retained its remarkable agility at altitude, and this was the reason for the type’s survival as an effective fighter over the Western Front up to the end of 1917 despite the fact that by the autumn of that year its performance and armament were wholly obsolete by the standards of the latest fighters in the theatre. In an effort to improve firepower, the pilots of No. 66 Squadron of the RFC added a Lewis gun to at least six of their Pup fighters during September, and in the following month some pilots of the RFC’s No. 54 Squadron fitted a Lewis gun on the centre section. This latter had to be discarded, however, as the centre section of the Pup was not stressed to take the gun. Although the Pup was withdrawn from first-line service over the Western Front by the end of 1917, production of the little Sopwith fighter was only then reaching its maximum rate. The greatest output was managed in the first quarter of 1918, when 500 Pups passed inspection. Most of these late-production Pups were delivered straight to training units, where the type was immensely popular because of its totally viceless handling characteristics. Production continued almost up to the time of the Armistice that ended World War I in November 1918, and official records indicate that 32 Pups passed inspection in the final quarter of 1918 before production ceased after the delivery of 1,896 aircraft.

Home Defence fighter
The Pup had been brought into service for home defence during July 1917, when No. 46 Squadron of the RFC was withdrawn from France and sent to Sutton’s Farm in Essex. This was a direct response to British public pressure for improved air defences after the second major bombing attack on London in the first week of July 1917, when 21 Gotha bombers dropped 72 bombs on the British capital, killing 57 people and injuring 193. The Gotha bombers did not return to London by day, however, and No. 46 Squadron returned to France at the end of August. Other Pup squadrons were formed specifically for home defence: No. 112 at Throwley in July 1917, and No. 61 at Rochford in August 1917. Only a few days later 16 Pup fighters of the latter unit took off to intercept 10 Gotha bombers that had flown over the east coast, but the bombers had a height advantage over the Pups and only a few of the British fighters managed to catch up with the German formation some 35 nm (40 miles; 64 km) from the English coast where, as a result of fuel shortages and gun troubles, the combats that did take place were inconclusive.

The official history implies that the home-defence version of the Pup was powered by the Gnome Monosoupape engine rated at 100 hp (74.6 kW), but it is doubtful whether all such Pup fighters had that engine. This variant of the Pup had the bottom segment of the engine cowling removed to assist the flow of exhaust gases, and there were four slots in the starboard upper quadrant of the cowling. The variant was dimensionally identical to the lower-power model, but differed in details such as its empty weight of 856 lb (388 kg), maximum take-off weight of 1,297 lb (588 kg), maximum speed of 95.5 kt (110 mph; 177 km/h) at sea level declining to 87 kt (100 mph; 161 km/h) at 15,000 ft (4570 m), climb to 6,500 ft (1980 m) in 7 minutes 5 seconds, service ceiling of 18,500 ft (5640 m), and endurance of 1 hour 45 minutes.

Away from the main theatre of war in France, the Pup was used operationally only by the RNAS in the Mediterranean area, where a few of the aircraft were flown by ‘C’ Squadron at Imbros and ‘F’ Squadron at Amberkoj and Marian. There can be little doubt that the 79 Pup fighters sent to the Middle East Brigade of the RFC were used only for training purposes at No. 5 Fighting School at Heliopolis in Egypt.

Seaborne service
In February 1917 the Grand Fleet Aircraft Committee that had been set up by Admiral Sir David Beatty presented a report in which, among other items, it recommended that the Pup should replace the Sopwith Baby floatplane in the aircraft carrier Campania as well as in Manxman as had already been decided. The committee also recommended that a number of light cruisers and other warships should be equipped to carry the Pup. These recommendations were made with a view to providing elements of the Grand Fleet with an effective anti-Zeppelin weapon.

A shipboard version of the Pup was therefore produced with a modified centre section incorporating a central cut-out to permit obliquely forward and upward fire by a single 0.303-in (7.7-mm) Lewis machine gun mounted on a tripod in front of the cockpit. As an alternative and/or addition, eight Le Prieur rockets could be carried on the interplane struts. This navalisation process also involved a number of other changes including the addition of the Mk I emergency flotation bags, which lay flat under the lower wing until inflated. The system of launching a Pup from a small platform was validated by Flight Commander F. J. Rutland, who achieved such a take-off for the first time in June 1917 when he lifted off from a raised platform between the bridge structure and a forward gun turret on the light cruiser Yarmouth, and in the following month Flight sub-Lieutenant B. A. Smart used the system to fly off Yarmouth for an interception that resulted in his destruction of the Zeppelin L-23. The success of the system in official eyes is indicated by the fact that it was decided in October 1917 that all light cruisers and battle-cruisers should be fitted with a flying-off platform for the use of a Pup.

The system was, of course, wasteful as the Pup had to alight on the water at the end of the flight, and although the flotation system was designed to provide enough buoyancy to hold the aeroplane on the water long enough for a ship to arrive and recover the machine, this sometimes did not happen and any recovered aeroplane needed considerable work before it could be restored to service. From an early stage, therefore, the Admiralty was interested in the concept of the true aircraft carrier with a flight deck large enough for aircraft to land as well as take-off, or alternatively two smaller flight decks with the forward deck reserved for take-off and the after deck for landing. The first ship fitted with a proper flight deck was the converted light battle-cruiser Furious, which was adapted in 1917 with a flight deck over the forward part of the ship ahead of the superstructure.

This required any landing aeroplane to sideslip onto the centreline after moving past the superstructure, and the first successful landing of this type was achieved by Squadron Commander E. H. Dunning in a Pup during August 1917 when, after initial uncompleted trials had revealed a small speed differential between the ship and aeroplane, rope toggles were added under the lower wing and fuselage so that the deck crew could reach up and help draw the aeroplane down onto the deck. Dunning was killed while attempting the third such landing when his Pup went over the starboard side of Furious’s bow and the intrepid pilot was drowned. This accident finally convinced the Admiralty that Furious should be further adapted with an after platform on which aircraft could land after a straight approach over the stern, even though this system was fraught with its own dangers as a result of the great turbulence of the air after it had flowed past the superstructure.

This led to much experimental work with landing gears and arrester wires, and in this effort the Pup was used extensively. The wheels were replaced by wooden skids in order to decelerate the aircraft after touchdown, and various arrangements of arrester wires, both longitudinal and transverse, were evaluated. The work was initiated at the Isle of Grain under Squadron Commander H. R. Busteed, using a dummy deck laid out on the aerodrome. One of the Pup aircraft employed in this task was a prototype, which was flown with wheels, a propeller guard, and a large hook designed to engage transverse arrester wires. At least one Pup had sprung skids and a hook pivoted under the aeroplane’s centre of gravity position, and another had fixed skids with a pronounced curve, horns to engage longitudinal wires, and an aft-mounted hook for transverse wires. Ultimately a rigid skid landing gear arrangement was standardised, each skid having two pairs of horns. This version of the Pup had the Admiralty designation Type 9901a, and 10 such aircraft were in service with units of the Grand Fleet at the end of October 1918.

A few Pup aircraft were supplied to some of the Allied powers. As a gift from the British government one machine was sent to Russia in 1917, and in the following year two aircraft were given to Greece. In March 1917 a Pup made a forced landing in the neutral Netherlands, and was then used for a time by the Netherlands army air service. Two Pups were reported to be on the strength of the US Navy in November 1919.

The Pup was officially declared obsolete for service with the Royal Air Force, created in April 1918 by the amalgamation of the RFC and RNAS, during December 1918, and disappeared rapidly after this time. At least 11 Pups were given to Australia as part of the Imperial Gift in 1919.

Specification

Sopwith Pup

Type: fighter

Accommodation: pilot in the open cockpit

Fixed armament: one 0.303-in (7.7-mm) Vickers fixed forward-firing machine gun with 500 rounds on the upper part of the forward fuselage with synchronisation equipment to fire through the propeller disc

Disposable armament: up to eight Le Prieur air-to-air rockets carried on the interplane struts, and up to 80 lb (36 kg) of disposable stores carried on one hardpoint under the fuselage rated at 80 lb (36 kg), and generally comprising four 20 lb (9.1 kg) Cooper free-fall bombs

Equipment: standard navigation equipment, plus an optical gun sight

Powerplant: one Le Rhône 9C air-cooled 9-cylinder piston engine rated at 80 hp (59.6 kW) for take-off

Fuel: 19.25 Imp gal (23.1 US gal; 87.5 litres)

Dimensions: span 26 ft 6 in (8.08 m); area 254.00 sq ft (23.60 m²); length 19 ft 3.75 in (5.89 m); height 9 ft 5 in (2.87 m); tailplane span 10 ft 1 in (3.07 m); wheel track 4 ft 7 in (1.40 m)

Weights: empty 787 lb (357 kg); maximum take-off 1,225 lb (556 kg)

Performance: maximum level speed ‘clean’ 97 kt (111.5 mph; 179.5 km/h) at sea level declining to 81.5 kt (94 mph; 151 km/h) at 15,000 ft (4570 m); climb to 2,000 ft (610 m) in 2 minutes 0 seconds, to 6,500 ft (1980 m) in 8 minutes 0 seconds, to 10,000 ft (3050 m) in 14 minutes 0 seconds, and to 16,100 ft (4905 m) in 35 minutes 0 seconds; service ceiling 17,500 ft (5335 m); endurance 3 hours 0 minutes

Operators: Australia (11+), Greece (2), Netherlands (1), Russia (1), UK (1,896) & USA (2+)

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