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".
At the time, German firms were producing a variety of record-breaking high-speed designs, such as the single-engined Heinkel He 70, and Rothermere wanted to recapture the title of fastest civilian aircraft, as well as to purchase such an aircraft himself.
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.

Since July 1933, Frank Barnwell, Bristol's chief designer, had been working on a small twin-engine low-wing monoplane design, initially intended to be powered by the sleeve-valve Bristol Aquila radial engine, designated as the Type 135.
Rothermere became aware of Bristol's proposal and, in response to his inquiry, 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 at an altitude of 6,500 feet.
By this point, proposed use of the Aquila engine had been shelved in favour of the supercharger-equipped, poppet-valve Bristol Mercury engine.
Deeming it suitable for the issued challenge, the design of Type 135 was further adapted to produce the Type 142 in order to meet the requirements outlined by Rothermere.
In late March 1934, Rothermere placed an order for a single 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, which had been given the name Britain First, conducted its maiden flight from Filton Aerodrome, South Gloucestershire.
Flight tests soon proved that the aircraft was in fact faster than any fighter in service with the Royal Air Force (RAF) at the time, having demonstrated a top speed of 307 mph.
Rothermere presented the aircraft to the nation for a formal evaluation at 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 suitable medium bomber.

Based upon talks from the conference, the Air Ministry quickly formalised Specification B.28/35 for prototypes of a bomber version; the Type 142M (M for military).
One principal 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 sizable bomb bay.
Other modifications included the addition of a bomb-aimer's position and a Browning machine gun in the nose along with provisions for a semi-retractable gun turret in the dorsal position.
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". At the time, German firms were producing a variety of record-breaking high-speed designs, such as the single-engined Heinkel He 70, and Rothermere wanted to recapture the title of fastest civilian aircraft, as well as to purchase such an aircraft himself. 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.
Since July 1933, Frank Barnwell, Bristol's chief designer, had been working on a small twin-engine low-wing monoplane design, initially intended to be powered by the sleeve-valve Bristol Aquila radial engine, designated as the Type 135. Rothermere became aware of Bristol's proposal and, in response to his inquiry, 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 at an altitude of 6,500 feet. By this point, proposed use of the Aquila engine had been shelved in favour of the supercharger-equipped, poppet-valve Bristol Mercury engine. Deeming it suitable for the issued challenge, the design of Type 135 was further adapted to produce the Type 142 in order to meet the requirements outlined by Rothermere. In late March 1934, Rothermere placed an order for a single 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, which had been given the name Britain First, conducted its maiden flight from Filton Aerodrome, South Gloucestershire. Flight tests soon proved that the aircraft was in fact faster than any fighter in service with the Royal Air Force (RAF) at the time, having demonstrated a top speed of 307 mph. Rothermere presented the aircraft to the nation for a formal evaluation at 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 suitable medium bomber.
Based upon talks from the conference, the Air Ministry quickly formalised Specification B.28/35 for prototypes of a bomber version; the Type 142M (M for military). One principal 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 sizable bomb bay. Other modifications included the addition of a bomb-aimer's position and a Browning machine gun in the nose along with provisions for a semi-retractable gun turret in the dorsal position.
Bristol Blenheim