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 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.

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.

[2] 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".

[2] 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.

[2] 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).

[3][2] 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).

The Air Ministry had chosen to order the type directly from the drawing board, having been urgently sought as one piece of a wider and rapid expansion of the RAF.

[13] Both the navigator's station and range limitations of the Blenheim Mk.I had been subject to considerable criticism, prompting the development of an improved model to rectify the shortcomings.

[13] On 24 September 1937, an experimental Blenheim Mk.I, modified with an extended forward fuselage beyond its original stepless cockpit, smooth-fronted nose enclosure, made its first flight from Filton.

[14] Another modification resulted in the Blenheim Mk III, which lengthened the nose, dispensing with the "stepless cockpit" format of the Mk.I, introducing a true windscreen in front of the pilot, to provide more room for the bomb aimer.

The tail unit is of a cantilever monoplane style, using an all-metal tailplane and fin while the aerodynamically-balanced rudder and elevators use a metal frame covered with fabric.

Most secondary instruments were arranged along the left side of the cockpit, essential items such as the propeller pitch control were actually placed behind the pilot where they had to be operated by feel alone.

[18] To achieve its relatively high speed, the Blenheim used a very small fuselage cross-section, with its upper front glazing all at one angle in the form of a "stepless cockpit" that used no separate windscreen panels for the pilot, a notable feature of a substantial majority of German bomber designs, first conceived during the war years.

[27] Shortly after the conflict's start, the RAF Advanced Air Striking Force (AASF) was deployed to numerous airfields in France, allowing for shorter range bombing missions against German targets, including industries.

[28] In May 1940, AASF and BEF Blenheims participated in the Battle of France, being sent against German forces moving towards Brussels, resulting in many aircraft quickly sustaining heavy damage or being lost to enemy fire.

[35] Typically operating from bases in the northern areas of the British mainland, such as RAF Lossiemouth, flying for extended periods over the North Sea led to the weather posing almost as much of a risk as enemy combatants, particularly as most of the Blenheim IVs lacked any heating or deicing systems; in response, some aircraft were later equipped with boilers fixed onto the starboard engine exhaust.

One Blenheim returned early (the pilot was later charged but was killed on another operation before a court martial was held); the other eleven, which reached Denmark, were shot down, five by flak and six by Bf 109s.

[40] On 12 August 1941, an action described by The Daily Telegraph in 2006 as being the "RAF's most audacious and dangerous low-level bombing raid, a large-scale attack against power stations near Cologne" took place.

[33] In April 1941, a campaign aiming to completely close off the Channel to enemy shipping was launched using an initial flight of Blenheims stationed at RAF Manston.

With this radar equipment, a Blenheim from the Fighter Interception Unit (FIU) at RAF Ford achieved the first success on the night of 2–3 July 1940, accounting for a Dornier Do 17 bomber.

By the end of 1940, a total of three RAF squadrons equipped with Blenheim IV aircraft were performing anti-shipping, bombing, and reconnaissance missions in support of Allied ground forces in North Africa.

[45] By July 1941, it had been recognised that, in response to the increasing intensity of combat in North Africa and in the Middle East theatres, additional squadrons were urgently required.

[33] By that point, the traditional daylight light bomber role was more effectively carried out by suitable fighter-bombers, and the surviving examples were relegated to training duties.

Nonetheless, the Blenheim played a role in preventing India from falling and in recapturing Burma, destroying over 60 aircraft on the ground in raids on Bangkok early in the campaign.

60 Squadron RAF was credited with shooting down Lt Col Tateo Katō's Nakajima Ki-43 fighter and badly damaging two others in a single engagement on 22 May 1942, over the Bay of Bengal.

[49] The Air Ministry's replacement for the Blenheim as a daylight bomber, another Bristol design, the Buckingham, was overtaken by events and changes in requirements, and considered inferior to the de Havilland Mosquito, and as such did not see combat.

[51] On 9 April 1942, nine Blenheims from 11 Squadron attacked the 1st Air Fleet (Kidō Butai); the Imperial Japanese main carrier battle group (Admiral Chūichi Nagumo).

[55][10] The Finns also received 20 half-completed ex-Yugoslavian Mk IV Blenheims captured by Germany, together with manufacturing tools, production equipment, and a huge variety of spare parts, although some of these had been damaged or otherwise destroyed through sabotage.

[citation needed] Data from British Warplanes of World War II,[65] The Bristol Blenheim I[18]General characteristics Performance Armament Avionics