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Bristol Types 142M / 149 / 160 Blenheim

The Bristol Blenheim is a British light bomber aircraft 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 Lord Rothermere to produce the fastest commercial aircraft in Europe.

The Type 142 first flew in April 1935, and the Air Ministry, ordered a modified design as the Type 142M  for the Royal Air Force (RAF) as a bomber.

Deliveries of the new 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, except in Canada where Fairchild Canada built the Type 149 under licence as the Bolingbroke.

The Type 160 Bisley was also developed from the Blenheim but was already obsolete when it entered service.

Both versions were converted into heavy fighters by the addition of a gun pack with four Browning .303 in (7.7 mm) machine guns mounted under the fuselage.

The Mk.IV was also used as a maritime patrol aircraft and both aircraft 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 most of the RAF’s biplane fighters in the late 1930s but advances soon left it vulnerable if flown in daylight, though it proved successful as a night fighter.

The Blenheim was effective as a bomber, but many were shot down.

Both Blenheim types were used by foreign operators and examples were licence built in Yugoslavia and Finland, in addition to Canada.


Blenheim Mk.I

Three-seat twin-engined light bomber, powered by two 840 hp (630 kW) Bristol Mercury VIII radial piston engines, armed with a 0.303 in (7.7 mm) machine gun in the port wing, plus a 0.303 in (7.7 mm) Vickers K gun in the dorsal turret, maximum bombload 1,000 lb (450 kg).

1,552 built.

Company designation Type 142M.

Blenheim Mk.IF

Night fighter version, equipped with an AI Mk III or Mk IV airborne interceptor radar, armed with four 0.303 in (7.7 mm) machine guns in a special gun pack under the fuselage.

 About 200 Blenheim Mk Is were converted into Mk IF night fighters.

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 905 hp (675 kW) Bristol Mercury XV radial piston engines, armed with a 0.303 in (7.7 mm) machine gun in the port wing, plus two 0.303 in (7.7 mm) machine-guns in a powered operated dorsal turret, and two remotely controlled rearward-firing 0.303 in (7.7 mm) machine guns mounted beneath the nose, maximum bombload 1,000 lb (450 kg) internally and 320 lb (150 kg) externally. 3,307 built.

Company designation Type 149

Blenheim Mk.IVF

Long-range fighter version, armed with four 0.303 in (7.7 mm) 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





42 ft 7 in (12.98 m)


56 ft 4 in (17.17 m)


9 ft 10 in (3.00 m)

Wing area

469 sq ft (43.6 m2)


RAF-28 (18%)

Empty weight

9,790 lb (4,441 kg)

Gross weight

14,400 lb (6,532 kg)


2 × Bristol Mercury XV 9-cylinder air-cooled radial piston engines,

920 hp (690 kW) each


3-bladed Hamilton Standard variable-pitch propellers, built under a license agreement (1935) by de Havilland


Maximum speed

266 mph (428 km/h, 231 kn) at 11,800 ft (3,600 m)

Cruise speed

198 mph (319 km/h, 172 kn)


1,460 mi (2,350 km, 1,270 nmi)

Service ceiling

27,260 ft (8,310 m)

Time to altitude

6,500 ft (2,000 m) in 4 minutes 10 seconds

Wing loading

30.7 lb/sq ft (150 kg/m2)


0.13 hp/lb (0.21 kW/kg)



1 × .303 in (7.7 mm) Browning machine gun in port wing



2 × .303 in (7.7 mm) Browning guns rear-firing in under-nose blister o


 Nash & Thompson FN.54 turret

2 × .303 in (7.7 mm) Browning guns in dorsal turret


1,200 lb (540 kg) total

4 × 250 lb (110 kg) General Purpose bombs 


2 × 500 lb (230 kg) GP bombs internally.


 8 × 40 lb (18 kg) GP bombs externally


T1082 (transmitter)


 R1083 (receiver) radio sets.

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