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Bristol B.149 Bristol B.160 Blenheim / Bolingbroke
The Blenheim had been designed, under the direction of Frank Barnwell, to provide the RAF with a high-speed light bomber, and a version had then been produced to provide the RAF with a replacement for the Hawker Demon turret fighter. The concept of a twin-engined multi-seat long-range fighter was to prove as flawed as the Boulton Paul Defiant.
The first all-metal cantilever monoplane of stressed-skin construction to enter production for the RAF, the Blenheim marked the beginning of a new era of equipment.
The Blenheim’s conversion from three-seat light bomber to heavy fighter in 1938 was prompted by what was considered as fully adequate. At the time of its introduction its performance allowed it to out-pace most contemporary service aircraft but early in the conflict it proved vulnerable to fighter attack, being deficient in defensive armament and armour, and performance.
The Bristol Type 142M provided armament, a bomb aimer's position, internal bomb stowage and more powerful 626kW Mercury VIII radial engines. To make room for a bomb bay in the lower fuselage, the low-wing configuration of the civil Type 142 was changed to mid-wing for the military version, which became named Blenheim.
The prototype made its first flight on 25 June 1936, and initial deliveries went to No 114 Bomber Squadron in March 1937.
 Blenheim Is of No.44 Sqn, RAF, 1938
The requirement for longer range led to evolution of the long-nosed, increased tankage and strengthened landing gear version, named originally Bolingbroke I. These began to enter RAF service in March 1939, by then designated Blenheim IV.
 Blenheim Mk.IV
By the outbreak of World War II Blenheim Is had been superseded by Mk IVs in the UK, but remained in first-line service in Greece and the Western Desert. A Blenheim made the first aerial sortie of the war when, on 3 September 1939, a machine of No 139 Squadron made a photo reconnaissance flight over the German fleet in the Schillig Roads. On the following day Blenheims and Well-ingtons joined in a mast-height bombing of the pocket battleship von Scheer. For the fighter role, the Blenheim was simply adapted from the standard Mk.I bomber by the addition of a ventral pack manufactured by the Southern Railway’s Ashford workshops, containing four 0.303in Browning guns plus 500 rounds of ammunition for each weapon. This supplemented the normal armament of a single wing-mounted Browning and a Vickers “K” 0.303 in a B.I. Mk.III semi-retractable hydraulically-operated dorsal turret. Some 200 Blenheims were modified to fighters, the first examples entering service with No,600 AAF Squadron at Hendon in September 1938.
Early operational experience with the Blenheim IF dictated the provision of a reflector sight, self-sealing tanks and some armour. No.23 Squadron undertook the first night intruder sortie of the war on 21-22 December 1939.
On 5 June 1940 the Luftwaffe made its first night attack on London, and Blenheim IFs instituted nocturnal patrols which, on 18 June, resulted in the destruction of five bombers.
Meanwhile, the Blenheim IF had been closely involved in the development of airborne intercept radar. A flight of three aircraft of No.600 Squadron operating from Manston had performed operational trials with AI Mk.III radar, and on the night of 2-3 July a Blenheim IF from the Fighter Interception Unit at Ford gained the first kill with this radar. The Blenheim would equip the first ever night-fighting unit in the world for the No.25 Squadron.
 Blenheim Is of No.603 Sqn, Northolt, April 1940
Subsequently the Blenheim IF became the prime night interceptor during 1940-41 and equipped six squadrons for Fighter Command in mid-1940 until supplanted by the Beaufighter.
 1940 experimental reconnaissance variant – lightened an unarmed
The Blenheim IV with which the RAF entered the second World War was an all-metal monoplane powered by two Bristol Mercury radial engines, each giving 920 hp. Carrying a crew of three, the Blenheim had a span of 56 ft 4 in (17.17 m). Maximum speed was 262 mph (422 km/h) and range 1,800 miles (2,895 km). A 1,000-lb (454-kg) bomb load could be carried and defensive armament included a pair of guns in a dorsal turret.
Bristol Blenheim IF
Blenheim IF
Engines: 2 x Bristol Mercury VIII, 840 hp
Empty weight: 8840 lb / 4100 kg
Loaded weight: 12.200 lb / 5534 kg
Max speed: 237 mph / 381 kph at SL
Max speed: 278 mph / 447 kph at 15,000 ft / 4572 m
Cruise speed: 315 mph / 346 kph at 15,000 ft
ROC: 1480 fpm / 451 m/min
Time to 5000ft / 1524m: 3.9 min
Time to 10,000ft / 3048m: 8.1 min
Service ceiling: 24,600 ft / 7498 m
Max range: 1050 mi / 1890 km
Armament: 5 x 0.303in Browning guns / 1 x Vickers “K” 0.303in mg
Bristol 160 Blenheim Mk IV
Blenheim V
Blenheim 5
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