Bristol Blenheim

The Bristol Blenheim is a British light bomber designed and built by the Bristol Aeroplane Company, which was used extensively in the first two years of the Second World War, with examples still being used as trainers until the end of the war. Development began with the Type 142, a civil airliner, after a challenge from the newspaper proprietor Lord Rothermere to produce the fastest commercial aircraft in Europe. The Type 142 first flew in April 1935, and the Air Ministry, ordered a modified design as the Type 142M for the Royal Air Force (RAF) as a bomber.

Deliveries of the new Blenheim to RAF squadrons commenced on 10 March 1937. In service the Type 142M became the Blenheim Mk.I which would be developed into the long-nosed Type 149, the Blenheim Mk.IV, except in Canada where Fairchild Canada built the Type 149 under licence as the Bolingbroke. The Type 160 Bisley was also developed from the Blenheim but was already obsolete when it entered service.

Both versions were converted into heavy fighters by the addition of a gun pack with four Browning .303 in (7.7 mm) machine guns mounted under the fuselage. The Mk.IV was also used as a maritime patrol aircraft and both aircraft were also used as bombing and gunnery trainers once they had become obsolete as combat aircraft.

The Blenheim was one of the first British aircraft with an all-metal stressed-skin construction, retractable landing gear, flaps, a powered gun turret and variable-pitch propellers. The Mk.I was faster than most of the RAF's biplane fighters in the late 1930s but advances soon left it vulnerable if flown in daylight, though it proved successful as a night fighter. The Blenheim was effective as a bomber but many were shot down. Both Blenheim types were used by foreign operators and examples were licence built in Yugoslavia and Finland, in addition to Canada.

In 1933 Frank Barnwell, Bristol's chief designer, went to the United States to collect first-hand information on their latest twin-engined, low-wing monoplane airliners. When he returned home he discussed one of them, the Lockheed Electra 12A, with Roy Fedden and prepared a design to match it using Fedden's Bristol Aquila engine which produced 500 hp, the same power as the engine used in the Electra. Sir Archibald Russell described Barnwell's design as "close to being a replica of the Electra". It was designated Type 135.

In early 1934, Lord Rothermere, owner of the Daily Mail newspaper, challenged the British aviation industry to build a high-speed aircraft capable of carrying six passengers and two crew members – he referred to the ambition as seeking "the fastest commercial aeroplane in Europe, if not the world". German firms were producing record-breaking high-speed designs, such as the single-engined Heinkel He 70, and Rothermere wanted the prestige of being able to claim to have the fastest civilian aircraft. Rothermere also intended to encourage businesses and key figures to make greater use of civil aviation and to demonstrate to the British Air Ministry how their fighter aircraft may not be able to match modern transport aircraft, which may be easily converted to, or used as the basis for, a bomber aircraft.

Rothermere became aware of Bristol's Type 135 proposal and on 3 March 1934, Barnwell issued him with a quote of the specification and performance statistics of the design, including an estimated top speed of 240 mph (390 km/h) at 6,500 ft (2,000 m). The Aquila engine had been shelved in favour of the supercharger-equipped, poppet-valve Bristol Mercury engine. Deeming it suitable for the challenge, the design of Type 135 was further adapted to produce the Type 142 to meet the requirements outlined by Rothermere. In late March 1934, Rothermere placed an order for a Type 142 aircraft, under which he paid for half of the estimated £18,500 cost up front and the remainder upon the aircraft's first flight in the following year.

On 12 April 1935, the Type 142, named Britain First, conducted its maiden flight from Filton Aerodrome, South Gloucestershire. Flight tests soon proved that the aircraft was faster than the fighters in service with the Royal Air Force (RAF), having a top speed of 307 mph (494 km/h). Rothermere presented the aircraft to the nation for a formal evaluation as a potential bomber. By June 1935, the Air Ministry had become interested in the project due to its high performance. On 9 July 1935, a design conference was held by Bristol at the ministry's request into the question of converting the Type 142 into a medium bomber.

The Air Ministry quickly formalised Specification B.28/35 for prototypes of a bomber version; the Type 142M (M for military). One change between the Type 142M bomber and its Type 142 predecessor was the repositioning of the wing from a low-wing to a mid-wing position, which allowed for more internal space within the fuselage underneath the main spar to accommodate a sizeable bomb bay. Other modifications included the addition of a bomb-aimer's position and a Browning machine gun in the port wing along with provisions for a semi-retractable gun turret in the dorsal position.