Vickers F . B . 5 The Vickers F . B . 5 ( Fighting Biplane 5 ) ( known as the " Gunbus " ) was a British two - seat pusher military biplane of the First World War . Armed with a single . 303 in ( 7 . 7 mm ) Lewis Gun operated by the observer in the front of the nacelle , it was the first aircraft purpose - built for air - to - air combat to see service , making it the world ' s first operational fighter aircraft . Design and development . Vickers began experimenting with the concept of an armed warplane designed to destroy other aircraft in 1912 . The first resulting aircraft was the " Destroyer " ( later designated Vickers E . F . B . 1 ) which was shown at the Olympia Aero Show in February 1913 , but crashed on its maiden flight . This aircraft was of the " Farman " pusher layout , to avoid the problem of firing through a tractor propeller , and was armed with a single belt - fed Vickers gun . The E . F . B . 1 was the first in a line of Vickers ' " Experimental Fighting Biplanes " , of which the F . B . 5 was the most famous - and the first to be built in quantity . While the " Destroyer " was a failure , Vickers continued to pursue the development of armed pusher biplanes , and their designer Archibald Low drew up a new design , the Vickers Type 18 , or Vickers E . F . B . 2 . This was a two - bay biplane powered by a single 80 hp ( 60 kW ) Gnome Monosoupape 9 - cylinder rotary engine with a steel tube structure , with fabric covered wings and tail , and a duralumin covered nacelle with large celluloid windows in the sides . The unequal - span wings were unstaggered , with lateral control by wing warping , while the aircraft had a large semi - circular tailplane . Armament remained a single Vickers gun mounted in the nose of the nacelle , with limited movement possible , and a very poor view for the gunner . The E . F . B . 2 made its first flight at Brooklands on 26 November 1913 . It was soon followed by the E . F . B . 3 , powered by a similar engine , but using ailerons instead of wing warping , and with equal - span wings , while the nacelle omitted the large windows fitted to the E . F . B . 2 . The belt feed proved problematic for a flexible machine gun , and the weapon installed was changed to the lighter , handier , drum - fed . 303 in ( 7 . 7 mm ) Lewis gun . The F . B . 5 first flew on 17 July 1914 . It was powered by a single 100 hp ( 75 kW ) Gnome Monosoupape 9 - cylinder rotary engine driving a two - bladed propeller , and was of simple , clean , and conventional design compared with its predecessors . In total , 224 F . B . 5s were produced , 119 in Britain by Vickers , 99 in France and 6 in Denmark . F . B . 6 . The Vickers F . B . 6 was a development of the F . B . 5 with an increased span on the upper wing . Only one was built . F . B . 9 . A further development of the F . B . 5 the Vickers F . B . 9 had a more streamlined nacelle and an improved ring mounting ( either Vickers or Scarf ) for the Lewis gun . 50 were delivered to Royal Flying Corps training units . A few served in some F . E . 2b squadrons while they were waiting for their new aircraft in late 1915 - very early 1916 . Operational history . The first F . B . 5 was delivered to No . 6 Squadron of the Royal Flying Corps ( RFC ) at Netheravon in November 1914 . On 25 December 1914 , the first use of the F . B . 5 in action took place , when F . B . 5 No . 664 took off from Joyce Green airfield to engage a German Taube monoplane , hitting the Taube ( and possibly causing its loss ) with incendiary bullets from a carbine after the Lewis gun jammed . Eighteen days later , the same flight crew , Second Lieutenants M . R . Chidson and D . C . W . Sanders , flying the first F . B . 5 in France , No . 1621 , were forced to land behind German lines , and the new plane fell into enemy hands . The F . B . 5 began to be seen on the Western Front when the first examples reached No . 2 Squadron RFC on 5 February 1915 . The type served in ones and twos with several other units before No . 11 Squadron RFC became the world ' s first fighter squadron when , fully equipped with the F . B . 5 , it deployed to Villers - Bretonneux , France on 25 July 1915 . Second Lieutenant G . S . M . Insall of 11 Squadron won the Victoria Cross for an action on 7 November 1915 in which he destroyed a German aircraft while flying a Gunbus . No . 18 Squadron RFC , which deployed to France in November 1915 , also operated the F . B . 5 exclusively . Early aircraft were fitted with British - built Monosoupapes , which proved less reliable than French - built engines , while much work was done before a useful gun mounting became available . Although its forward - firing machine gun was a great advantage , the fighter did not have the speed or rate of climb to pursue its quarry ; thus , the F . B . 5 ' s performance proved to be inadequate for its intended role . This can be illustrated by noting only the single pilot / observer team of Lionel Rees and James McKinley Hargreaves became aces while flying this type . By the end of 1915 , it was outclassed by the Fokker " Eindecker " . Some examples of the improved Vickers F . B . 9 were sent to France , pending sufficient supplies of the Royal Aircraft Factory F . E . 2 b , but the active career of the Gunbus was soon over . The remaining examples were mostly used as trainers . Legacy . The Vickers company persisted with an active experimental program during the First World War period , including a line of single - seat pusher fighters , but the F . B . 5 remained their only significant production aircraft until the Vickers Vimy bomber , which entered service too late to have an impact on the war . Despite its moderate effectiveness , the Vickers F . B . 5 did have a lasting legacy as German pilots continued to refer to British pusher aircraft as " Vickers - types " . Many victories over D . H . 2 or F . E . 2b pushers were reported as destruction of a " Vickers " .