The S.E.5 was the work of a small Farnborough team — Henry Folland and John Kenworthy as designers, with chief test pilot Frank Goodden deeply involved — built around Marc Birkigt’s new 150 hp Hispano-Suiza 8 V8. Goodden first flew it on 22 November 1916. The early prototypes had a roomy, heavily glazed cockpit and a wing that proved too weak: Goodden was killed on 28 January 1917 when a prototype broke up in the air. The wings were strengthened and the large windscreen cut down, and the definitive S.E.5a followed with the 200 hp engine. Building the fighter around the advanced but temperamental geared Hispano-Suiza was a gamble that nearly cost the programme its place at the front — and was rescued by the home-grown Wolseley Viper.

The S.E.5 used conventional two-bay wooden wings, wire-braced and fabric-covered, on a wooden fuselage. The first prototypes, however, had wings that were structurally suspect: on 28 January 1917 chief test pilot Frank Goodden was killed when a prototype broke up in the air. The wing was redesigned and strengthened before the type went to war, and the reworked structure proved tough enough to let pilots dive the S.E.5a hard in combat — a quality that defined its fighting style. The heavily framed original windscreen was also cut down to improve the view.

The S.E.5a was built around the 200 hp geared Hispano-Suiza 8b, but that engine’s reduction gearing was troublesome and supply from France and licensees was chronically short, stranding finished airframes through late 1917. The rescue came from Wolseley’s Viper — a high-compression, direct-drive development of the Hispano that was reliable and simple to mass-produce — which became the standard fit. Direct-drive 200 hp Hispano engines (and, for US-built machines, the Wright-Martin) were also used. Engine type mattered: a good Viper transformed the aircraft’s reputation from unreliable to trusted.

Pilots exploited the S.E.5a’s speed, ceiling and stability rather than its turn. The classic attack was a diving pass from above, using height and momentum, then a zoom-climb back to safety — tactics that suited its strong airframe and steady gun platform. James McCudden fitted high-compression engines and refined his machine to reach and ambush high-flying German reconnaissance aircraft; Mannock built disciplined formation tactics around it. The overwing Lewis on its Foster mount gave a second option: pull it down and fire upward into an enemy’s unprotected underside.

The original S.E.5 (1916–17) used the 150 hp Hispano-Suiza and a large, heavily framed cockpit canopy. The S.E.5a was the definitive mass-production fighter: a strengthened airframe, cut-down windscreen and a nominal 200 hp engine — the geared Hispano-Suiza 8b, direct-drive Hispano, or the standard Wolseley Viper. In the United States, licence production was ordered from Curtiss and others; relatively few were completed before the Armistice. After the war the American S.E.5E was built and rebuilt by Eberhart with the Wright-Martin engine, and a number of aircraft were converted into two-seaters or used for skywriting and racing.

No reliable unit price for the S.E.5a is preserved in the usual references — wartime aircraft were bought under bulk government contracts spread across many firms, and figures were not consistently recorded or published. Any single 1917–18 “price tag” should be treated with caution. As a modern reference point, operating an airworthy S.E.5a reproduction — vintage or replica V8 engine, specialist maintenance, insurance and hangarage — is commonly estimated at very roughly $2,000–4,000 per flight hour. That figure is an informed estimate for comparison only, not a historical cost, and real-world numbers vary widely between operators.