The design originated from the Air Ministry Specification G.4/31 which called for a general purpose aircraft, capable of carrying out level bombing, army co-operation, dive bombing, reconnaissance, casualty evacuation and torpedo bombing. The biplane Vickers Type 253 design, which used a radical geodesic airframe construction, derived from that used by Barnes Wallis in the airshipR100, was ordered by the Ministry and tested against the specification along with the Fairey G.4/31, Westland PV-7, Handley Page HP.47, Armstrong Whitworth A.W.19, Blackburn B-7, Hawker P.V.4 and the Parnall G.4/31. The Type 253 was declared the winner, with 150 being ordered. The Vickers Type 246monoplane, which used the same geodetic design principles for the fuselage and wings, was then built as a private venture, first flown at Brooklands by Vickers' Chief Test PilotJ "Mutt" Summers, on 19 June 1935 and offered to the RAF. This aircraft had superior performance but did not attempt to meet the multi-role requirements of the specification, being designed as a bomber only. An initial order for 96 Type 246s was substituted for the Type 253 order. The RAF ultimately ordered a total of 176 with the service name "Wellesley", to a newly written specification 22/35, with a 14-month production run starting in March 1937. The Wellesley was a single-engine monoplane with a very high 8.83 aspect ratio wing and a manually operated, retractable undercarriage. As it was not known how the geodetic structure could cope with being disrupted by a bomb bay, the Wellesley's bomb load was carried in two streamlined panniers under the wings. The Wellesley Mk I had two cockpits but this was slightly changed in what was unofficially dubbed the Wellesley Mk II, whose pilot's canopy was extended to cover the navigator/bomb aimer's position that had been buried in the fuselage. Only the pilot had flight controls. The gunner retained a separate canopy.
Operational history
The RAF received its first Wellesleys in April 1937: they served with No. 76 Squadron RAF at Finningley. The aircraft eventually equipped six RAF Bomber Command squadrons in the UK. Five aircraft with provisions for three crew members were modified for long-range work with the RAF Long-Range Development Flight. Additional modifications included the fitting of Pegasus XXII engines and extra fuel tanks. On 5 November 1938, three of these aircraft under command of Squadron Leader Richard Kellett flew non-stop for two days from Ismailia, Egypt to Darwin, Australia setting a world distance record. All three aircraft broke the record, but No. 2 aircraft landed in West Timor, short of the objective. The Wellesley's record remained unbroken until November 1945. This flight is still the longest by an aircraft with a single piston engine. By the outbreak of the Second World War, the Wellesley had been phased out from home-based squadrons, with only four examples remaining in Britain, but they remained in service with three squadrons based in the Middle East. Following the Italian declaration of war on 10 June 1940, the remaining Wellesley squadrons participated in the East African Campaign against Italian forces in Eritrea, Ethiopia and Somaliland. Although obsolete, the Wellesley formed a major part of the British Commonwealth bomber forces, mainly carrying out raids targeting Eritrea and northern Ethiopia. Sudan-based Wellesleys carried out their first bombing mission on 11 June 1940, against Asmara in Eritrea. Three days later, they were involved in their first air combat, when CapitanoMario Visintini, future top-scoring biplane ace of the Second World War, intercepted a pair of Wellesleys from 14 Squadron on their way to bomb Massawa. Visintini, who was flying a Fiat CR.42, shot down the aircraft K7743, flown by Pilot Officer Reginald Patrick Blenner Plunkett. It was the first of Visintini's 16 air victories in Eastern Africa. In the early part of the campaign, fighter escort was not available and when caught by CR.42s, Wellesleys proved vulnerable to the Italian biplane fighter. Despite this, the Wellesley continued to be sent on bombing raids, bombing Addis Ababa from Aden on 18 August. The Wellesley continued in use against the Italians over East Africa until November 1941, when Gondar, the last Italian-held town, fell to Commonwealth and Ethiopian forces. The final Wellesley-equipped unit, 47 Squadron, was then switched to maritime reconnaissance duties over the Red Sea, continuing in this role until September 1942. While the Wellesley was not a significant combat aircraft, the design principles that were tested in its construction were put to good use with the Wellington medium bomber, which became one of the mainstays of Bomber Command in the early years of the European war. In February 1940, three Wellesleys were sold to Egypt to serve in the Royal Egyptian Air Force.
