The Folland Aircraft Company's Gnat fighter, designed by W.E.W. (Teddy) Petter, was a private venture development of the Folland Midge and the prototype (G-39-2) first flew in 1955. Petter's concept was for a lightweight fighter to capitalise on the range of new, modern jet engines combined with a simply engineered fuselage and wing, making it affordable and easy to manufacture with a minimum of engineering resources. The company promptly commenced work, privately financing the project, which received the designation Fo-141, later named Folland Gnat. The design was strongly influenced by Operational Requirement OR.303, which sought a capable lightweight fighter aircraft. Development went ahead, irrespective of external orders or financing from any British government department including the Ministry of Supply.
New lightweight turbojet engines enabled the concept to be realised. Initially, the Gnat was intended to be powered by a Bristol BE-22 Saturn turbojet engine. Unfortunately, further development of the Saturn was cancelled, so the more capable Bristol Orpheus turbojet was adopted instead. However, this engine was not fully available at the time, so in order to avoid further delay, the Gnat was fitted with the less powerful Armstrong Siddeley Viper 101 turbojet. Using a different powerplant between prototypes and production aircraft is not ideal, so Folland created a 'proof-of-concept' demonstrator, designated the Folland Fo-139 Midge. With an almost identical airframe and very similar avionics, this would test and verify the design in advance of the full prototype being built.
The Midge (G-39-1) was first flown at Boscombe Down on 11th August 1954, piloted by the company's chief test pilot Edward Tennant. Despite its low-powered engine, the Folland Midge could exceed Mach 1 in a dive and proved to be very agile during its test programme. Sadly on 20th September 1955, the Midge was destroyed in a crash at Chilbolton, and claimed the life of Swedish test pilot Max Mathez, who had clipped some trees on take-off.
Due to the Midge's development as a private venture and coupled with its short lifespan, there was a disappointing lack of interest from the RAF, although senior officers did encourage the design of a similar aircraft, specifically for fast-jet training. As it happened, Folland had an enlarged version of his original light-fighter concept, the Gnat. This differed from the Midge with larger air-intakes suitable for the proposed Bristol Orpheus engine, a slightly larger wing and provision for a 30 mm ADEN cannon in each intake lip.
The prototype Folland Fo.140 Gnat F.1 (G-39-2) first flew at Boscombe Down on 18th July 1955 and following favourable reports, six aircraft were ordered by the Ministry of Supply for evaluation purposes. Although the Ministry of Supply evaluation brought no orders, and the Hawker Hunter eventually won the competition, the Gnat was also assessed in 1958 as a replacement for the de Havilland DH.112 Venom. In the same year, orders for Gnat F.1 and FR.1 variants were placed by Finland (13 aircraft) and Yugoslavia (two aircraft). Although there were plans for F.3 and F.4 variants, these were never built. India also placed a large order for the type and initial aircraft were produced and first flown in the UK during 1958. The aircraft was so successful with the Indian Air Force that within two years, a licencing agreement was in place for Hindustan Aeronautics Limited to manufacture 175 aircraft.
Greater success was seen with the two-seat Folland Fo.142 Gnat Trainer, especially after the take-over of the company by Hawker Siddeley. XM691, the first of 14 development aircraft, was first flown from Chilbolton on 31st August 1959. At last, production turned towards reasonable numbers with orders coming from the Ministry of Aviation between 1960 and 1962. In all, 432 airframes bearing the Gnat designation were built in six main variants, plus India's licence-built HAL Ajeet fighter and trainer. The Folland Fo.144 Gnat T.1 is the most famous variant, being the aircraft chosen for the world-famous RAF aerobatic display team, the Red Arrows, and its1964-1965 predecessor the Yellowjacks. Gnats were operated by the Red Arrows from 1965 until replaced by the British Aeropspace Hawk T.1 in 1979.
RAF pilots graduated from basic training on the Hunting Percival - BAC Jet Provost and, once they had gained their wings, they were selected for one of three streams: fast-jet, multi-engine or rotary (helicopters) aircraft. Those selected for fast-jets were posted to RAF Valley on Anglesey where they had advanced training on the Folland Gnat T.1. After gaining sufficient experience (normally around 70 hours) they progressed to the Hawker Hunter.
Following the introduction of the Hawker Siddeley Hawk in the RAF training role in April 1976, the Gnats were withdrawn from service. The largest operator, No.4 Flying Training School at RAF Valley, retired its last Gnat in November 1978. All serviceable aircraft were then sent to No. 1 School of Technical Training at RAF Halton and other surplus Gnats became ground instructional airframes at smaller training establishments. The RAF eventually retired the Gnat training airframes with many being sold to private operators.