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 bomber development as the Type 142M for the Royal Air Force (RAF).

Deliveries of the 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, while in Canada Fairchild Canada built the Type 149 under licence as the Bolingbroke. The Type 160 Bisley was also developed from the Blenheim.

Both versions were converted into heavy night fighters by the addition of a gun pack with four Browning machine guns mounted under the fuselage. The Mk.IV was also used as a maritime patrol aircraft and both versions 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 the RAF's biplane fighters in the late 1930s but advances soon left it vulnerable if flown in the day, though it proved successful as a night fighter. Both Blenheim types were used by foreign operators and examples were licence built in Canada, Yugoslavia and Finland.

Development

Origins

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

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, including an estimated top speed of at . Rothermere presented the aircraft to the nation for a formal evaluation as a bomber. In June 1935, the Air Ministry showed interest due to its performance. On 9 July 1935, a design conference was held by Bristol at the ministry's request to convert the Type 142 into a bomber.

From July 1936 onwards, various additional orders were placed for the Blenheim Mk.I, including multiple orders for the export market. In order to meet the demand, secondary assembly lines were established at Chadderton by Avro and at Speke by Rootes Securities. Other countries also procured the Blenheim, including Romania, Greece and Turkey. The Bolingbroke, which had been developed in response to Air Ministry Specification G.24/35 to procure a coastal reconnaissance bomber as a replacement for the Avro Anson, had substantial improvements that would serve as the basis for improved variants of the Blenheim. 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.

In early 1939, the first batch of Blenheim Mk.IVs were accepted into service; these lacked outer fuel tanks but were accepted due to the urgent demand for the type. Early Blenheim Mk.IVs were also equipped with the Mercury VIII engine, most were fitted with the more powerful Mercury XV or Mercury 25 models. Further aircraft deliveries were made to the production standard and were primarily manufactured by Avro and Rootes. Production of the Blenheim IV continued until June 1943, when newcomers such as the Beaufort-derived Beaufighter had succeeded the type.

The Blenheim typically carried a crew of three – pilot, navigator/bombardier and wireless (radio) operator/air gunner. The pilot's quarters on the left side of the nose were so cramped that the control yoke obscured all flight instruments while engine instruments eliminated the forward view on landings. 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. The navigator/bombardier was seated alongside the pilot, and made use of a sliding/folding seat whilst performing the bomb aiming role. Dual flight controls could be installed. The raid was a failure, only nine aircraft attacked, and only superficial damage was done to the cruiser Emden, when one of No. 107 Squadron's Blenheims crashed into the cruiser, killing 11 crewmen. RAF Coastal Command were soon using the Blenheim to protect British shipping convoys off the east coast. Several squadrons of Blenheim IVs were assigned to the AASF, being frequently used against targets in France and the Low Countries once the Battle of France had begun. Blenheims were also assigned to the air component of the British Expeditionary Force of the Army. German attacks upon the French airfields also damaged a considerable number of Blenheims on the ground. On 14 May, a combined force of Fairey Battles and Blenheims was dispatched on a counter-attack on German forces breaking through defensive lines but 40 out of 71 aircraft were lost in this sortie. This is the worst losses proportionally taken by the RAF. Around 50 Blenheims supported the Dunkirk evacuation by harassing enemy forces.

Rapid advances in technology in the late 1930s rendered the Blenheim obsolescent by 1939. In particular, it had become heavier as extra service equipment was installed that was found to be necessary through operational experience. This, coupled with the rapid performance increases of the fighters that would oppose it, had eclipsed the Blenheim's speed advantage. In January 1941, the Air Staff classified the Blenheim as inadequate in terms of performance and armament for current operations.

Home front

Blenheim squadrons were still in demand after their withdrawal from France as part of the British action during the Norwegian campaign. Typically operating from bases in northern Britain, 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 heating or deicing systems and in response, some aircraft were fitted with boilers on the starboard engine exhaust. Heavy losses occurred, caused by both enemy action and engine failures due to icing.

Blenheim units operated throughout the Battle of Britain, often taking heavy casualties, although they were never accorded the publicity of the fighter squadrons. From July to December 1940, Blenheims raided German-occupied airfields both in daylight and at night. Although most of these raids were unproductive, there were some successes; on 1 August five out of twelve Blenheims sent to attack Haamstede and Evere (Brussels) were able to bomb, damaging (50 per cent, 40 per cent and 10 per cent) three Bf 109Es of II./JG 27 at Leuwarden and apparently killing a Staffelkapitän identified as Hauptmann Albrecht von Ankum-Frank. Two other 109s were claimed by Blenheim gunners. Another successful raid on Haamstede was made by a single Blenheim on 7 August which destroyed one 109 of 4./JG 54, heavily damaged another, and caused lighter damage to four more.

There were also some missions which produced an almost 100% casualty rate amongst the Blenheims. One such operation was mounted on 13 August 1940 against a Luftwaffe airfield near Aalborg in north-western Denmark by twelve aircraft of 82 Squadron. One Blenheim returned early (the pilot was later charged but was killed on another operation before a court martial was held) while the other eleven, which reached Denmark, were shot down, five by flak and six by Bf 109s. Blenheim units had also been formed to carry out long-range strategic reconnaissance missions over Germany and German-occupied territories. In this role, the Blenheims once again proved to be too slow and vulnerable against Luftwaffe fighters and they took constant casualties.

thumb|Wreckage of a Blenheim shot down over the Occupied Netherlands on 15 February 1941

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. The raid was a low-level daylight raid by 54 Blenheims under the command of Wing Commander Nichol of 114 Squadron. They hit their targets (Fortuna Power Station in Oberaußem-Fortuna and the Goldenberg Power Station in Hürth-Knapsack), but twelve of the Blenheims were lost during the raid, 22% of those that took part, which was far above the sustainable loss rate of less than 5%. The England cricketer Squadron leader Bill Edrich was awarded the DFC for his part in the raid.

From 5 September 1940 Blenheims of Bomber Command began a bombing campaign targeting German-occupied ports along the English Channel, alongside heavier bomber types. Bomber Command Blenheims also performed anti-shipping patrols due to Coastal Command's own strike squadrons being heavily depleted throughout the latter half of 1940. On 11 March 1940, a Blenheim IV, P4852, became the first RAF aircraft to sink a U-boat, having scored two direct hits on in the Schillig Roads. 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. Between April and June that year, a total of 297 Blenheims of No 2. Group attacked German shipping at sea, losing 36 aircraft, while Coastal Command launched 143 attacks in the same period, losing 52 aircraft; by the end of the year, 698 ships had been attacked and 41 of these sunk for the loss of 123 aircraft. Upon the outbreak of the Pacific War in December 1941, some Blenheim squadrons in the Middle East were relocated from the theatre to the Far East in response to the new threat from Japanese forces.

South East Asia

thumb|Blenheims of [[No. 60 Squadron RAF flying low to attack a Japanese coaster off Akyab, Burma on 11 October 1942]]

Blenheims continued to operate widely in many combat roles until about 1943, equipping RAF squadrons in the UK and at British bases in Aden, India, British Malaya, Singapore, and the Dutch East Indies. Many Blenheims were lost to Japanese fighters during the Malayan Campaign and the battles for Singapore and Sumatra.

One Blenheim pilot, Squadron Leader Arthur Scarf, was posthumously awarded the Victoria Cross for an attack on Singora, Thailand, on 9 December 1941. Another bomber of No. 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. Katō's death was a severe blow to the Imperial Japanese Army Air Force.

The Air Ministry's replacement for the Blenheim as a medium day 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. The final ground-attack version – the Blenheim Mk.V – first equipped 139 Squadron in June 1942. Eventually thirteen squadrons – mainly in the Middle East and Far East – received this variant but generally operated them only for a few months.

One Blenheim Mk.IV left in Java by the retreating British forces in 1942 ended up in the hands of the fledgling Indonesian Air Force (AURI). They repaired it, installed Nakajima Sakae engines, painted it in their colours, and flew it around Yogyakarta on at least three occasions.

First attack on the Japanese carrier force

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). The Blenheims approached undetected by the A6M2 Zero combat air patrol (CAP) fighters and surprised the Japanese carrier battle group. While the bombers attacked fleet carrier from an altitude of , they missed. This was the first time a Japanese carrier force had faced a concerted air attack in the Pacific War.

thumb|Blenheim I (BL-111) coming in for a landing on Luonetjärvi Airfield, March 1944. BL-111 was a Series I aircraft with doorless bomb bays.

The Finnish Blenheims flew 423 missions during the Winter War, and close to 3,000 missions during the Continuation War and Lapland War. Blenheim machine-gunners also shot down eight Soviet aircraft. Thirty-seven Blenheims were lost in combat during the wars.

After the war, Finland was prohibited from flying bomber aircraft by the Paris Peace Treaty, with Finland's Blenheims being placed into storage in 1948. However, in 1951, five Blenheims were re-activated for use as target tugs, with the last flight of a Finnish Blenheim taking place on 20 May 1958. The usual nickname of Blenheim in the Finnish Air Force was Pelti-Heikki ("Tin Henry").

Variants

thumb|Bristol Blenheim Mk.I in flight

thumb|Bolingbroke IVT in the Commonwealth Air Training Plan Museum, Brandon, Manitoba

;Blenheim Mk.I : Three-seat twin-engined light bomber, powered by two Bristol Mercury VIII radial piston engines, armed with a machine gun in the port wing, plus a Vickers K gun in the dorsal turret, maximum bombload . 1,552 built. Company designation Type 142M.

;Blenheim Mk.IF : Long-range heavy fighter version, armed with four machine guns in a special gun pack under the fuselage. About 200 Blenheim Mk.Is were converted into Mk.IF fighters, with a number of those converted to night fighters with the addition of AI Mk.III or Mk.IV airborne interceptor radar.

;Blenheim Mk.II : Long-range reconnaissance version with extra fuel tankage. One built.

;Blenheim Mk.III : Prototype for Mk.IV with lengthened nose.

;Blenheim Mk.IV/Bolingbroke I: Improved version, fitted with protective armour and extended nose, powered by two Bristol Mercury XV radial piston engines, armed with a machine gun in the port wing, plus two machine-guns in a powered operated dorsal turret, and two remotely controlled rearward-firing machine guns mounted beneath the nose, maximum bombload internally and externally. 3,307 built. Company designation Type 149

;Blenheim Mk.IVF : Long-range fighter version, armed with four machine guns in special gun pack under the fuselage. About 60 Blenheim Mk.IVs were converted into Mk.IVF fighters.

;Blenheim Mk.V/Bisley Mk.I: High-altitude bomber, powered by two Bristol Mercury XV or XXV radial piston engines. Company designation Type 160

Operators

thumb|Blenheim IV BL-200 (with the [[Western use of the swastika in the early 20th century#Finland|Finnish Hakaristi markings) at the Aviation Museum of Central Finland]]

25px Canada

An airworthy Blenheim was rebuilt from a scrapped Bolingbroke over a 12-year period, only to crash at an airshow at Denham within a month of completion in 1987.

A replacement Bolingbroke Mk.IVT was rebuilt to flying status over five years and painted to represent a Blenheim Mk.IV in wartime RAF service. It began flying in the UK in 1993, and was used in the 1995 film version of Shakespeare's Richard III. This aircraft crashed on landing at Duxford on 18 August 2003, but after extensive repair and conversion to the Mark I "Short nose" version, was displayed and flown again in 2014, at the Imperial War Museum Duxford, England. The aircraft appeared in the 2017 Christopher Nolan film Dunkirk.

In summer 1996, a Bristol Blenheim Mk.IVF was recovered from the sea, off Rethymnon, Crete. The No. 203 Squadron RAF aircraft was downed by friendly fire on 28 April 1941. The Blenheim was moved to the Hellenic Air Force Museum for restoration.

The Kent Battle of Britain Museum in Hawkinge began a project to rebuild a Blenheim IVF using the remains of four Bolingbrokes in 2018. The Aircraft Restoration Company (ARC) provided surplus parts from its own Blenheim restoration.

The Royal Museum of the Armed Forces and Military History in Brussels exhibits a Bolingbroke painted as a No. 139 Squadron RAF Blenheim XD-A that crash landed in May 1940 in Belgium.

Specifications (Blenheim Mk.IV)

thumb|3-view drawing of the Blenheim Mk.I(F), with scrap views showing the Mk.IV and Mk.V variants

References

Citations

Bibliography

External links

RAF Bristol Blenheim history
No. 211 Squadron RAF
Blenheim Society
Aircraft Restoration Company
Finnish Mk.IV Blenheim restoration
"Up in the Blenheim, a civilian pilot's impressions..."; Flight, 24 June 1937
"How the Bristol Blenheims are erected"; Aircraft Engineer (supplement to Flight), 19 May 1938
"In the air IV – Flying the Blenheim"; Flight, 15 November 1945