Dubbed unofficially the Streamline Gunbus, the F.B.9, which emerged towards the end of 1915, introduced numerous refinements over its predecessor, the F.B.5. The fuselage nacelle was of improved aerodynamic form; the wings and tailplane sported rounded tips; streamlined Rafwires replaced stranded steel cables and turnbuckles for interplane bracing, and a plain, Vee-type undercarriage supplanted the twin skids previously used.

The standard power plant remained the 100hp Gnome Monosoupape rotary. Vickers (Wells Aviation) built a total of 95 F.B.9s (5271 to 5290 and A1411 to A1460) plus the prototype (7665), and a further 24(7812 to 7835) were built by Darracq in France, some of which were issued to the RFC (No 11 Sqn) and were used during the Battle of the Somme which began on 1 July 1916. The manufacture of the F.B.9 in Italy by Vickers-Terni fell through owing to political reasons.
The only FB.9s known to have seen operational service were seven examples (Serials 7812, 7813, 7820, 7826, 7827 and 7828), all of which were flown on war patrols by 11 Squadron RFC in France in June July 1916. On July 1, 7828 gained a confirmed aerial combat victory. All other FB.9s were relegated to RFC and RNAS training units, where they gave faithful service until late 1918. As trainers, several FB.9s were modified to have dual controls, and many had a Scarff ring fitted in the front cockpit for gunnery practice. At least one FB.9 was armoured and fitted with an oleo undercarriage. None remained on charge at the time of the Armistice.

Engine: 100 hp Gnome Monosoupape rotary, or 110 hp Le Rhone rotary
Span: 10.3 m (33 ft 9 in)
Length: 8.7 m (28 ft 5.5 in)
Height: 3.5 m (11 ft 6 in)
Wing area: 31.59 sq.m / 340.03 sq ft
Max take-off weight: 858 kg / 1892 lb
Empty weight: 467 kg / 1030 lb
Maximum speed: 132.9 km/h (82.6 mph) at ground level
Climb to 3048 m (10000 ft): 51 min
Service ceiling: 3353 m (11000 ft)

FB.9
Engine: Gnome Monosoupape, 100 hp
Wingspan: 33 ft 10 in
Wing area:
Length: 27 ft 10 in
Height: 7 ft 0 in
Empty weight: 1029 lb
Loaded weight: 1892 lb
Wing loading:
Max speed: 79 mph at 6500 ft
Service ceiling: 11,000 ft
Endurance: 5 hr
Rate of climb: 19 min to 6500 ft
Armament: 1 x Lewis gun
Crew: 2

Progressive changes introduced by successive E.F.B.3s led to the E.F.B.5 – the E.F.B.4 being a project with a more streamlined nacelle centred between the wings and only two tailbooms – which was flown from Joyce Green to Brooklands on 17 July 1914. In parallel, Vickers developed the E.F.B.6, which, basically similar to the E.F.B.5, had longer-span upper wings. It lacked top decking between the two crew seats and had ailerons in the upper wings only. At Brooklands on 14 July 1914, the E.F.B.6 was taken on strength by the Royal Flying Corps when World War I began, but was not developed.

No orders were received but Vickers felt certain that war was imminent and began building 50 F,B.5s. These were eventually taken over by the RFC, which put a total of 241 in service. The E.F.B.5 was ordered into production for both the RFC and the RNAS on 14 August 1914, the first series aircraft being completed in the following October. At this time, the aircraft became simply F.B. (Fighting Biplane) 5 and was dubbed Gunbus. The E.F.B.5 had retained the semi-circular tail-plane of the E.F.B.2 and early E.F.B.3, but the series F.B.5 had an enlarged tailplane of rectangular planform and a larger rudder. A Lewis gun on a more practical mount supplanted the similar-calibre Vickers in the nose and the standard power plant was the 100hp Gnome Monosoupape nine-cylinder rotary.

The true fighter squadron was born on the 14 February 1915 when No.11 Squadron was formed at Netheravon. Completely equipped with Vickers FB5 aircraft this was the first unit established purely with the intention of destroying other aircraft.

The first F.B.5 reached the Western Front early February 1915, and, on the following 25 July, the first squadron of any air service formed specifically for fighting duties and equipped throughout with a single aircraft type arrived in France, this being the RFC’s No 11 Sqn with F.B.5s.

The RNAS made little use of the F.B.5, and, after the delivery of four to that service, the large majority of subsequent deliveries went to the RFC, although the RNAS did receive two further F.B.5s which, ordered in May 1915, were fitted with the 150hp Smith Static radial engine, its large diameter propeller necessitating the raising of the fuselage nacelle several inches above the lower wing. Two hundred and forty-one F.B.5s were delivered to the RFC, of which 109 were sent to the British Expeditionary Force in France (60 in 1915 and 49 in 1916). Licence production of the F.B.5 was undertaken in France by the Societe Anonym Darracq (which built a total of 99 of these and the later F.B.9) between May 1915 and June 1916. Twelve were also built under licence in Denmark in 1917-18 by the Tojhusvasrksted. At least four F.B.5As were built with armour-plated fuselage nacelles and these were powered by 110hp Clerget 9Z nine-cylinder rotary engines and had oleo undercarriages. Suffering an unreliable engine and a marginal performance throughout its operational career, the F.B.5 was finally withdrawn from the Western Front in the autumn of 1916, being subsequently confined to RFC instructional units.

Built by members of the Vintage Aircraft Flying Association for eventual display at the RAF Museum, a Gunbus reproduction was powered by a Gnome 100 hp Mono rotary with original prop.

The Vintage Aircraft & Flying Assoc. FB.5 Gunbus was built in 1966 at Weybridge. Registered G-ATVP c/n VAFA.01, it first flew at Wisley on 14 June 1966. It was stored for a short while at Henlow but then went on display in the RAF Museum at Hendon.

Gallery

Engine One 100 hp Gnome Monosoupape
Length 27 ft 2 in (8.25m)
Wing span 36 ft 6 in (11.1m)
Height: 3.38 m / 11 ft 1 in
Wing area: 35.49 sq.m / 382.01 sq ft
Weight empty 1,220 lb (553 kg)
Max take-off weight: 930 kg / 2050 lb
Max speed: 70 mph (113 kph) at 5000 ft
Range: 402 km / 250 miles
Service ceiling: 9,000 ft (2,700 m) fully loaded
Endurance 4.5 hours
Seats: 2
Armament: One Lewis machine gun, plus small bombs

FB.5
Engine: Gnome Monosoupape, 100 hp
Wingspan: 36 ft 6 in
Wing area: 362 sq.ft
Length: 27 ft 2 in
Height: 11 ft 0 in
Empty weight: 1220 lb
Loaded weight: 2050 lb
Wing loading: 5.4 lb/sq.ft
Max speed: 60 mph at 5000 ft
Service ceiling: 9000 ft
Endurance: 4 hr
Rate of climb: 19 min to 6500 ft
Armament: 1 x Vickers mg
Crew: 2