In December 1914, the Sopwith Aviation Company designed a small, two-seat biplane powered by an Gnome rotary engine, which became known as the "Sigrist Bus" after Fred Sigrist, the Sopwith works manager. The Sigrist Bus first flew on 5 June 1915 and although it set a new British altitude record on the day of its first flight, only one was built, serving as a company runabout.[2] [3]
The Sigrist Bus formed the basis for a new, larger, fighter aircraft, the Sopwith LCT (Land Clerget Tractor), designed by Herbert Smith and powered by a Clerget engine. Like the Sigrist Bus, each of the upper wings (there was no true centre section) was connected to the fuselage by a pair of short (half) struts and a pair of longer struts, forming a "W" when viewed from the front; this giving rise to the aircraft's popular nickname of the Strutter.[1] The first prototype was ready in mid-December 1915, undergoing official testing in January 1916.[3] [4]
The Strutter was of conventional wire-braced, wood and fabric construction. The pilot and gunner sat in widely separated tandem cockpits, with the pilot in front, giving the gunner a good field of fire for his Lewis gun. The aircraft had a variable-incidence tailplane that could be adjusted by the pilot in flight and airbrakes under the lower wings to reduce landing distance.[2] [5]
The Vickers-Challenger synchronisation gear was put into production for the Royal Flying Corps (RFC) in December 1915 and in a few weeks, a similar order for the Scarff-Dibovski gear was placed for the RNAS.[6] [7] Early production Strutters were fitted with one or the other of these gears for the fixed .303-in Vickers machine gun; due to a shortage of the new gears some early aircraft were built with only the observer's gun. Later aircraft were either fitted with the Ross or the Sopwith-Kauper gears.[8] No early mechanical synchronisation gear was reliable and it was not uncommon for propellers to be damaged or shot away.
The Scarff ring mounting was also new and production was at first slower than that of the aircraft requiring them. Various makeshift Lewis mountings as well as the older Nieuport ring mounting, were fitted to some early Strutters as a stopgap.[9] The two-seaters could carry four bombs underwing, which could be replaced by two bombs for anti-submarine patrols.[10] From the beginning, a light bomber version was planned, with the observer's cockpit eliminated to allow more fuel and bombs to be carried in the manner of the Martinsyde Elephant and the B.E.12, with an internal bomb bay capable of carrying four bombs.[10] [11]
The prototype two seater flew in December 1915 and production deliveries started to reach the RNAS in February 1916.[4] By the end of April, No. 5 Wing RNAS had a flight equipped with the new aircraft. The Sopwiths were used to escort the wing's Caudron G.4 and Breguet Bre.4 bombers and for bombing.[12] [13] The War Office had ordered the type for the RFC in March but because Sopwith's production capacity was contracted to the navy, the RFC orders had to be placed with Ruston Proctor and Vickers.[14] Sub-contract production from these manufacturers did not get into its stride until August. Since the Battle of the Somme was planned for the end of June and with the RFC having a shortage of modern aircraft, it was agreed that a number of Sopwiths would be transferred from one service to the other, allowing 70 Squadron to reach the front by early July 1916 with Sopwith-built Strutters, originally intended for the Navy.[15]
At first, 70 Squadron did very well with their new aircraft. The period of German ascendency known as the Fokker scourge was over and the Strutter's long range and excellent armament enabled offensive patrolling deep into German-held territory.[16] By the time 45 Squadron reached the front in October, the new Albatros fighters were arriving at the German: [[Jagdstaffel]]n. By January 1917, when 43 Squadron arrived in France, the Strutter was outclassed as a fighter; a more powerful Clerget 9B improved performance slightly but too late to reverse the situation.[17] It was still a useful long-range reconnaissance aircraft when it could be provided with adequate fighter escort but was one of the types to suffer severely during "Bloody April", 43 squadron alone suffering 35 casualties, from an officer establishment of 32.[18]
Like other early Sopwith types, the Strutter was very lightly built and its structure did not stand up very well to arduous war service. It was far too stable to make a good dogfighter and the distance between the pilot and the observer's cockpits impeded their communication. The last operational Strutters in the RFC were replaced by Sopwith Camels in late October 1917.[19]
The type's long range and stability were good qualities for a home defence fighter and it served with 37, 44 and 78 squadrons. Most of the Strutters supplied to home defence units had been built as two-seaters but many were converted locally to single-seaters to improve performance. Some of these single-seaters were similar to the bomber variant but others were of a different type, known (like similarly adapted Sopwith Camels) as the Sopwith Comic. The cockpit was moved back behind the wings and one or two Lewis guns, either mounted on Foster mountings or fixed to fire upwards, outside the arc of the propeller, replaced the synchronised Vickers.
The RNAS used most of their Strutters as bombers (in the Aegean and Macedonia as well as in France) and as shipboard aircraft, where it was known as the Ship's Strutter and flew from aircraft carriers, other warships of the Royal Navy and . The RNAS and the RFC (and after April 1918 the Royal Air Force [RAF]) used the type as a trainer after it had been withdrawn from operational service and like the Sopwith Pup, it proved a popular personal aircraft for senior officers.
The largest user of the Sopwith was actually the French French: Aéronautique Militaire. By May 1916 it was obvious that the pusher Farman and Breguet bombers and reconnaissance aircraft were obsolete and with the failure of their tractor aircraft replacements, particularly the Nieuport 14, the Sopwith was ordered in large numbers from French manufacturers in three versions, the SOP. 1A.2 (two-seat reconnaissance), SOP. 1B.2 (two-seat bomber) and SOP. 1B.1 (single-seat bomber).[20] While in French service, they equipped a large portion of the French bomber and artillery-observation squadrons and carried out many bombing attacks against industrial and military targets, including the German front lines. It was not as successful against fighters, suffering substantial casualties and downing fewer enemy aircraft than either the aircraft used before it or after. With the belated introduction of the Breguet 14 A.2 and B.2, the last of the Sopwiths were withdrawn from operational service in early 1918 although they would continue in service with training units until after the end of the war.
Three Belgian squadrons also flew French-built Sopwiths, and surplus French Sopwiths were used by several countries postwar. During the war, several Strutters that were interned after landing in the Netherlands were purchased for the Dutch Dutch; Flemish: Luchvaart Afdeeling.
Over 100 Strutters were also built in Russia by Duks and Lebedev,[21] supplemented by large numbers delivered directly from Britain and France. The Strutter remained in large scale use by both the Soviet forces and White Russians during the Russian Civil War and Polish-Soviet war.[22] Three were captured during this war and used by the Poles in 1919–1920.[23] Other captured ones were used by Baltic states.
The American Expeditionary Force purchased 384 two-seat Strutter observation aircraft and 130 single-seat bombers from France in 1917–18.[24] While mainly used for training, they were used operationally by the 90th Aero Squadron as an interim measure, due to a shortage of later types.[25] The U.S. Navy used a number of the two-seat Sopwiths, along with Nieuport 28s and Hanriot HD.1s and 2s as ships' aircraft in the early postwar years, testing the use of aircraft from platforms mounted on the turrets of battleships.
The Strutter also served with the Imperial Japanese Army Air Force – some examples serving in the Japanese expeditionary force in Siberia during 1918.
Around 1,500 Strutters were built for the Royal Flying Corps and the Royal Naval Air Service and between 4,200 and 4,500 were built in France.
Original Sopwith Strutter aircraft are preserved at the following locations.[40]
Lithuania
Romania