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Bristol Blenheim

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When the twin-engined Blenheim bomber first appeared, its modern appearance and speed installed the belief in the Royal Air Force that they possessed the best bomber in the world. But when the Second World War broke out in September 1939 this was no longer the case and the type suffered heavy losses during unescorted daylight raids during the early part of the conflict. The Bristol Blenheim served the RAF for seven years at home and overseas.

Quick Facts
Bristol Blenheim side profile image
First flight
12th April 1935
Entered service
10th March 1937
Total built

Front view
Blenheim front view photo
Side view
Blenheim side view photo
Rear view
Sorry, no view photo available

The owner of the Daily Mail during the 1930s Lord Rothermere had a very keen interest in aviation, and in 1934 wanted an aircraft for his own use. The aircraft would need to have space for six passengers and two crew members with a good top speed. Frank Barnwell at the Bristol Aeroplane Company had a design outline for a twin-engined light transport aircraft. Powered by the 650-hp Bristol Mercury VIS engine, the Type 142, as it was known, made its maiden flight on the 12th April 1935 from Filton. Faster than any Royal Air Force fighter currently in service, the Air Ministry were interested in the aircraft and after being allowed to evaluate the type it was revealed to the nation and was called 'Spirit of Britain'.

With the Air Ministry looking at the aircraft as a potential light bomber Bristol would work on a militarised version designated the Type 142M. The main changes made to the design were the addition of a dorsal turret, bomb bay and bomb-aimer's station. The company submitted this idea to the Air Ministry, which they accepted. So under Specification 28/35 an initial order for 150 was placed in September 1935. Named the Blenheim, it would have a crew of three, pilot, navigator/bomb-aimer and air gunner/radio operator and on the 25th June 1936 the prototype flew for the first time.

The Blenheim Mk I was powered by the 840-hp Bristol Mercury VIII engine. This gave the aircraft a top speed of 285 mph, a range of 1,125 miles with a service ceiling of 32,000 ft. Armament consisted of a 0.303-in machine-gun located in the port wing and a Vickers 'K; gun in the dorsal turret. Deliveries of the aircraft started on the 10th March 1937 when No. 114 Squadron based at RAF Wyton began to receive theirs. This was followed four months later in July 1937 by an order for a further 434 aircraft.

By the time the Second World War (1939 – 1945) broke out in September 1939 only a handful of Blenheim Mk Is were being used as bombers by home based squadrons, the type being moved into other roles. Some would serve as both crew and conversion trainers whilst 200 were converted to night fighters and designated Blenheim Mk IF. This would see the aircraft fitted with additional armament in the form of four 0.303-in machine-guns fitted in a pack underneath the fuselage. Also installed was either Mk III or Mk IV Airborne Interception radar and it was a Blenheim Mk IF of the Fighter Interception Unit based at RAF Tangmere which, on the 23rd July 1940, shot down the first enemy aircraft using Airborne Interception radar, a Dornier Do 17.

In August 1935 the Air Ministry issued Specification G.24/35 which required an aircraft which would be used for coastal reconnaissance and as a light bomber and was intended to replace the Avro Anson. The design Bristol submitted was based on the Blenheim Mk I and was known as the Type 149. With the installation of Bristol Aquila engines it was intended to increase the range of the aircraft without the need for additional fuel tanks. However, this design was rejected by the Air Ministry.

Despite this initial rejection, the Air Ministry again looked at the Type 149 design but as a general reconnaissance aircraft. This would see a Blenheim Mk I used as the base with a number of changes made. Firstly the nose of the fuselage was increased so the navigator/observer had more room and additional fuel tanks added. This flew for the first time on the 24th September 1937. With the pressing need for Blenheims there was concern at the Air Ministry that production would be hindered if the Type 149 was ordered. Instead it would be sent to Fairchild Aircraft, Canada where the type would be built for the Royal Canadian Air Force and named the Bolingbroke.

Another change of heart by the Air Ministry saw them again consider the Type 149, this time as a stopgap as a torpedo bomber until, another Bristol design, the Beaufort was able to enter service. Known as the Blenheim Mk IV they had bigger fuel tanks in the wings and the Bolingbroke's longer nose design. Powered by the 920-hp Bristol Mercury XV engine, it had a top speed of 295 mph, range of 1,950 miles and a service ceiling of 31,500 ft. Armament was three 0.303-in machine-guns, one in the port wing and two in the dorsal turret. Bomb load was 1,320lb, the bomb load was increased by bomb racks under the wings which could hold 320lb bombs in addition to the 1,000lb in the bomb bay. The Blenheim Mk IV would enter service on the 19th January 1939 with No. 53 Squadron based at RAF Odiham and would see widespread service, not only with Bomber Command but also Fighter Command and Coastal Command.

On the day Britain declared war on Germany, 3rd September 1939, a Blenheim Mk IV from No. 139 Squadron became the first British aircraft of the war to fly over Germany when it undertook a reconnaissance sortie over Wilhelmshaven to monitor the German fleet. This was followed on the 4th September 1939 by one of the first attacks on German targets when shipping at Wilhelmshaven was bombed by Blenheims from Nos. 107 and 110 Squadron. Two squadrons Nos. 114 and 139 would be sent to France as part of the Royal Air Force's Advanced Air Striking Force and would operate alongside the Fairey Battle. Losses for the aircraft would be high as they operated during daylight and not always with fighter escort. One such mission on the 14th May 1940 saw five out of eight Blenheims fail to return from a raid on the Sedan bridgehead.

After Operation Dynamo (26th May 1940 - 4th June 1940), the evacuation of Dunkirk, the Battle of Britain (10th July 1940 - 31st October 1940) would begin and the Blenheim and its crews would undertake raids on German airfields in occupied Europe and invasion barges located in occupied ports. As with some of their missions in France the aircraft would be operating unescorted in daylight hours. Losses again were high with one raid on Aalborg airfield, Denmark on the 13th August 1940 seeing 100% losses when none of the 11 Blenheims of No. 82 Squadron sent returned, and of the 33 airmen only 13 survived as prisoners of war.

With the introduction of newer and faster aircraft the Blenheims time with home based Bomber Command squadrons came to an end in 1942, this wasn't the end of the types frontline service as they continued to serve overseas, not only with the Royal Air Force but other air forces including the Free French and Finnish.

The final variant to be produced was the Blenheim Mk V, which for a while was named the Bisley. Powered by the 950-hp Bristol Mercury 25 engine, its top speed was 260 mph, range 1,600 miles with a service ceiling of 31,000 ft. Armament was four 0.303-in machine-guns, two in the dorsal turret and two rear-firing in a blister under the nose. Bomb load was 1,000lb. Ten overseas squadrons based in the Middle East and Far East would receive the aircraft, with deliveries beginning during the summer of 1942.

In total 4,422 Blenheims were built.

Technical Details

Click on the aircraft image to view a larger version.

Top Speed Range Service Ceiling Armament
Blenheim Mk I 285 mph 1,125 miles 32,000 ft one 0.303-in machine-gun
one Vickers 'K' gun
1,000lb bombs
Blenheim Mk I side profile image
Blenheim Mk II Single Blenheim Mk I featuring a number of changes, including the installation of long-range fuel tanks.
Blenheim Mk IV 295 mph 1,950 miles 31,500 ft three 0.303-in machine-guns
1,320lb bombs
Blenheim Mk V 260 mph 1,600 miles 31,000 ft four 0.303-in machine-guns
1,000lb bombs


Click on a photo to view a larger version.
Blenheim Mk I
Blenheim Mk IV

See This Aircraft

(C) = Cockpit only exhibit. (F) = Fuselage only exhibit. (R) = Remains of an aircraft.

Blenheim Mk I Imperial War Museum, Duxford
Blenheim Mk ? (C)
Blenheim Mk IV Kent Battle of Britain Museum
Blenheim Mk IV Lincolnshire Aviation Heritage Centre
Bolingbroke Mk IV (C) Manx Aviation Preservation Society
Bolingbroke Mk IVT National Museum of Flight, Scotland
Blenheim Mk IV Royal Air Force Museum, Midlands

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