World War II: Bristol Blenheim

RAF Bristol Blenheim bombers
Bristol Blenheims. Public Domain

The Bristol Blenheim was a light bomber used by the Royal Air Force during the opening years of World War II. One of the first modern bombers in the RAF's inventory, it conducted the first British air attacks of the conflict, but soon proved highly vulnerable to German fighters. Outclassed as a bomber, the Blenheim found new life as a radar-equipped night fighter, maritime patrol aircraft, and a trainer. The type was largely withdrawn from frontline service by 1943 as more advanced aircraft became available.


In 1933, the chief designer at the Bristol Aircraft Company, Frank Barnwell, began preliminary designs for a new aircraft capable of carrying a crew of two and six passengers while maintaining a cruising speed of 250 mph. This was a bold step as the Royal Air Force's fastest fighter of the day, the Hawker Fury II, could only achieve 223 mph. Creating an all-metal monocoque monoplane, Barnwell's design was powered by two engines mounted in a low wing.

Though dubbed the Type 135 by Bristol, no efforts were made to build a prototype. This changed the next year when noted newspaper owner Lord Rothermere took an interest. Aware of advances overseas, Rothermere was an outspoken critic of the British aviation industry which he believed was falling behind its foreign competitors.

Seeking to make a political point, he approached Bristol on March 26, 1934, regarding purchasing a single Type 135 in order to have a personal aircraft superior to any flown by the RAF. After consulting with the Air Ministry, which encouraged the project, Bristol agreed and offered Rothermere a Type 135 for £18,500. Construction of two prototypes soon began with Rothermere's aircraft dubbed the Type 142 and powered by two Bristol Mercury 650 hp engines.

Bristol Blenhiem Mk. IV


  • Length: 42 ft. 7 in.
  • Wingspan: 56 ft. 4 in.
  • Height: 9 ft. 10 in.
  • Wing Area: 469 sq. ft.
  • Empty Weight: 9,790 lbs.
  • Loaded Weight: 14,000 lbs.
  • Crew: 3


  • Power Plant: 2 × Bristol Mercury XV radial engine, 920 hp
  • Range: 1,460 miles
  • Max Speed: 266 mph
  • Ceiling: 27,260 ft.


  • Guns: 1 × .303 in. Browning machine gun in port wing, 1 or 2 × .303 in. Browning guns in rear-firing under-nose blister or Nash & Thomson FN.54 turret, 2 × .303 in. Browning guns in dorsal turret
  • Bombs/Rockets: 1,200 lbs. of bombs

From Civil to Military

A second prototype, the Type 143, was also built. Slightly shorter and powered by twin 500 hp Aquila engines, this design was ultimately scrapped in favor of the Type 142. As development moved forward, interest in the aircraft grew and the Finnish government inquired regarding a militarized version of the Type 142. This led to Bristol beginning a study to assess adapting the aircraft for military use. The result was the creation of the Type 142F which incorporated guns and interchangeable fuselage sections which would allow it to be used as transport, light bomber, or ambulance.

A twin-engine Bristol Blenheim bomber at an airfield.
Bristol Blenhiem prototype. Public Domain 

As Barnwell explored these options, the Air Ministry expressed interest in a bomber variant of the aircraft. Rothermere's aircraft, which he dubbed Britain First was completed and first took to sky from Filton on April 12, 1935. Delighted with the performance, he donated it to the Air Ministry to help push the project forward.

As a result, the aircraft was transferred to the Aeroplane and Armament Experimental Establishment (AAEE) at Martlesham Heath for acceptance trials. Impressing the test pilots, it achieved speeds reaching 307 mph. Due to its performance, civil applications were discarded in favor military. Working to adapt the aircraft as a light bomber, Barnwell raised the wing to create space for a bomb bay and added a dorsal turret featuring a .30 cal. Lewis gun. A second .30 cal machine gun was added in the port wing.

Designated the Type 142M, the bomber required a crew of three: pilot, bombardier/navigator, and radioman/gunner. Desperate to have a modern bomber in service, the Air Ministry ordered 150 Type 142Ms in August 1935 before the prototype flew. Dubbed the Blenheim, the named commemorated the Duke of Marlborough's 1704 victory at Blenheim.

A row of Bristol Blenhiem bombers lines up on a the runway in Singapore.
Bristol Blenhiems of No. 62 Squadron at Singapore, February 1941.  Public Domain


Entering RAF service in March 1937, the Blenheim Mk I was also built under license in Finland (where it served during the Winter War) and Yugoslavia. As the political situation in Europe deteriorated, production of the Blenheim continued as the RAF sought to re-equip with modern aircraft. One early modification was the addition of a gun pack mounted on the aircraft's belly which featured four .30 cal. machine guns.

While this negated the use of the bomb bay, it allowed the Blenheim to be used a long range fighter (Mk IF). While the Blenheim Mk I series filled a void in the RAF's inventory, problems quickly arose. Most notable of these was a dramatic loss of speed due to the increased weight of the military equipment. As a result, the Mk I could only reach around 260 mph while the Mk IF topped out at 282 mph.

To address the problems of the Mk I, work began on what was eventually dubbed the Mk IV. This aircraft featured a revised and elongated nose, heavier defensive armament, additional fuel capacity, as well as more powerful Mercury XV engines. First flying in 1937, the Mk IV became the most produced variant of the aircraft with 3,307 built. As with the earlier model, the Mk VI could mount a gun pack for use as the Mk IVF.

Operational History

With the outbreak of World War II, the Blenheim flew the RAF's first wartime sortie on September 3, 1939 when a single aircraft made a reconnaissance of the German fleet at Wilhelmshaven. The type also flew the RAF's first bombing mission when 15 Mk IVs attacked German ships in Schilling Roads. During the war's early months, the Blenheim was the mainstay of the RAF's light bombers forces despite taking increasingly heavy losses. Due to its slow speed and light armament, it proved particularly vulnerable to German fighters such as the Messerschmitt Bf 109.

Blenheims continued to operate after the Fall of France and raided German airfields during the Battle of Britain. On August 21, 1941 a flight of 54 Blenheims conducted an audacious raid against the power station at Cologne though lost 12 aircraft in the process. As losses continued to mount, crews developed several ad hoc methods for improving the aircraft's defenses. A final variant, the Mk V was developed as a ground attack aircraft and light bomber but proved unpopular with crews and saw only brief service.

A New Role

By mid-1942, it was clear that the aircraft were too vulnerable for use in Europe and the type flew its last bombing mission on the night of August 18, 1942. Use in North Africa and the Far East continued through the end of the year, but in both cases the Blenheim faced similar challenges. With the arrival of the De Havilland Mosquito, the Blenheim was largely withdrawn from service.

The Blenheim Mk IF and IVFs faired better as night fighters. Achieving some success in this role, several were fitted with the Airborne Intercept Mk III radar in July 1940. Operating in this configuration, and later with the Mk IV radar, Blenheims proved capable night fighters and were invaluable in this role until the arrival of the Bristol Beaufighter in large numbers. Blenheims also saw service as long-range reconnaissance aircraft, thought they proved as vulnerable in this mission as when serving as bombers. Other aircraft were assigned to Coastal Command where they operated in a maritime patrol role and aided in protecting Allied convoys.

Outclassed in all roles by newer and more modern aircraft, the Blenheim was effectively removed from frontline service in 1943 and used in a training role. British production of the aircraft during the war was supported by factories in Canada where the Blenheim was built as the Bristol Fairchild Bolingbroke light bomber/maritime patrol aircraft.

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Your Citation
Hickman, Kennedy. "World War II: Bristol Blenheim." ThoughtCo, Aug. 28, 2020, Hickman, Kennedy. (2020, August 28). World War II: Bristol Blenheim. Retrieved from Hickman, Kennedy. "World War II: Bristol Blenheim." ThoughtCo. (accessed May 29, 2023).