Blackburn T7B 3MR4 construction
The prototype Blackburn T.7B (or 3MR4) under construction at Brough in 1929.
The Mitsubishi B2M naval attack aircraft had been procured as a replacement for the wooden Mitsubishi B1M. Intended for Japanese production, the Imperial Japanese Navy sought to ensure its success by seeking tenders for prototypes from British manufacturers.
The Blackburn Aircraft Company design, the Blackburn T.7B (Japanese designation 3MR4), was a large, three seat all-metal two-bay biplane powered by a single 625 hp Mitsubishi-Hispano-Suiza Type 51-12Lbr engine. Effectively, the Blackburn T.7B was an enlarged version of the Blackburn Ripon which had already been under development for the Fleet Air Arm.
A single British-built prototype was completed for final inspection on 29th November 1929, being flown for the first time on 28th December, before being shipped and arriving in Japan in February 1930.
Blackburn T7B 3MR4 prototype Japanese markings
Prototype Blackburn T.7B in Japan with two 250 lb bombs between the undercarriage legs.
The three crew (for reconnaissance operations) sat in separate cockpits comprised of a pilot, a wireless operator / bomb-aimer and an observer / gunner. For torpedo operations, this was reduced to two crew, with the fuel load being limited to 100 gallons.
In addition to the torpedo, armament also consisted of a fixed, forward-firing Vickers gun on the port side , with twin Lewis guns fired from the rear cockpit. An optional fourth gun could be carried, fired through an opening in the floor of the centre cockpit. With full fuel (and no torpedo), two 250 lb bombs could also be carried between the undercarriage legs.
Blackburn’s Chief Engineer travelled to Japan to oversee the manufacture and development of the initial production aircraft. A number of minor issues needed to be resolved before the third, locally-built version was adjudged to have met the Japanese Navy requirements. The type was then adopted as the Navy Type 89-1, although it was also known as the Mitsubishi B2M1 when it was fitted with a 650 hp Mitsubishi-Hispano Type 7 engine.
Blackburn T7B 3MR4 flying
The prototype Blackburn T.7B (3MR4) flying in Japan in 1930.
The Japanese-built aircraft adopted a rounded fin and rudder shape and a retractable coolant radiator.
The Blackburn-built prototype was lost in an accident when it was inadvertently flown without the main engine oil cock having been selected ‘on’.
As initially built, the type suffered from poor serviceability and a series of modifications in 1934. These changes resulted in the Mitsubishi B2M2 which was used extensively for bombing attacks against China at the start of the second Sino-Japanese War in 1937.
A total of 205 Mitsubishi B2M1 / B2M2 aircraft were built in Japan, the B2M2 variant being armed with two guns and an increased bomb load over short ranges. It also featured a triangular fin and rudder, a reduced wingspan and revised nose lines.
The type served on Japanese carriers from 1933 until 1937 and was also used in the training role.


Variants & Number Built

Prototypes  One only Blackburn T.7B                                                                                   
Production 205 aircraft as B2M1 and B2M2



  Blackburn T.7B (Recce) Mitsubishi B2M1 Mitsubishi B2M2
Powerplant One 625 hp Hispano-Suiza Type engine One 650 hp Mitsubishi-Hispano Type 7 engine
Span 49 ft 3.5 in 49 ft 11 in 49 ft 1 in
Maximum Weight 7,500 lb   7,936 lb
Capacity & Armament Three crew; one forward-firing Vickers gun, two rear Lewis guns in rear cockpit, optional gun below centre cockpit; 2 X 250 lb bombs. Three crew, one fixed Vickers plus one Lewis gun and up to 1,764 lb bomb load
Maximum Speed 135 mph at sea level 132 mph at sea level 140 mph at sea level
Cruise speed 115 mph 112 mph 119 mph
Range 800 miles 1,100 miles 1,090 miles




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