Mitsubishi Ki 46 'Dinah'
In 1937, the Japanese
firm of Mitsubishi Heavy Industries Company delivered a new
reconnaissance aircraft, the "Ki-15", to the Japanese Imperial Army.
The Ki-15 was a clean, single-seat, single-engine monoplane with fixed
landing gear and excellent range, and though it appeared useful enough
for the moment, the Technical Branch of the Imperial Army Air
Headquarters (Koku Hombu) knew that other nations were developing
fighters fast enough to overtake and destroy it.
Within two months of
the first service delivery of the Ki-15, the Koku Hombu began work on
the specifications for its successor, an improved reconnaissance
aircraft that was to discreetly overfly lands belonging to Japan's
potential adversaries. The requirements that were defined by the Koku
Hombu's Major Yuzo Fujita and his staff were aggressive, dictating an
aircraft with a top speed of 600 KPH (373 MPH) at 4,000 meters (13,100
feet). This was much faster than any Japanese aircraft that had flown
to that time.
The new aircraft also
was to have an endurance of six hours at 400 KPH (250 MPH) at an
altitude of 4,000 to 6,000 meters (13,100 to 19,700 feet). The Army air
staff knew that building an aircraft with such capabilities would not
be easy, and so gave industry designers a generally free hand in
designing whatever they thought could do the job. The aircraft could
have one or two engines, using air-cooled radials in the 560 to 710 kW
(750 to 950 HP) class, such as the Nakajima Ha-20-Otsu, Nakajima Ha-25,
or Mitsubishi Ha-26.
* Mitsubishi was
already designing a fast twin-engined reconnaissance aircraft
designated the "Ki-40", a variant of the company's proposed Ki-39
twin-engine fighter. Because of their established work, Mitsubishi was
awarded the contract for the new reconnaissance aircraft by the Koku
Hombu on 12 December 1937.
Although the Ki-40
hadn't been flown by that time, the Mitsubishi design team, led by
Tomio Kubo and Joji Hattori, realized very quickly that there was no
way it could be fast enough to meet the Koku Hombu specification. They
junked the Ki-40 design, retaining only some of its features in a new,
much more streamlined and elegant twin-engine aircraft with low-mounted
The new design was
given the designation "Ki-46". It featured a forward crew compartment
for the pilot and a separate crew compartment facing the rear for the
radio operator, with the two compartments separated by a bay containing
cameras and a large fuel tank with a capacity of 1,660 litres (440 US
gallons). The unusual crew accommodations were dictated by the need to
put the big fuel tank at the centre of gravity. It had "tail-dragger"
landing gear, with a retractable tailwheel and the main gear retracting
back into the engine nacelles.
The twin powerplants
were Mitsubishi Ha-26-Ko 14-cylinder air-cooled radial engines with
single-speed superchargers, with each engine providing 746 kW (900 HP).
The Nakajima Ha-25 radial was lighter and more powerful, but Mitsubishi
preferred to supply their own engines.
The Mitsubishi design
team had worked with the Aeronautical Research Institute of the
University of Tokyo to perform wind-tunnel tests for streamlining the
aircraft and in particular to optimize the engine fit, coming up with
aerodynamic, close-fitting cowlings and large spinners fitted over the
three-bladed constant-speed variable-pitch propellers. The tight
cowlings also improved the pilot's field of view.
* Despite such efforts,
when flight trials began in 1939 with Major Fujita at the controls, the
Ki-46 did not meet the speed requirements requested by the Koku Hombu,
attaining only 540 KPH (335 MPH) at 4,000 meters (13,100 feet). The
Koku Hombu still found it an excellent aircraft in all other regards,
and so the Ki-46 was accepted for production as the "Army Type 100
Command Reconnaissance Aircraft Model 1 (Ki-46-I)".
The Koku Hombu did
specify that Mitsubishi was to immediately begin work on a faster
version, the "Ki-46-II". Since the Ki-46-I's relatively low performance
meant that it was in principle vulnerable to interception, the
back-seat position was fitted with a single moveable Type 89 7.7
millimetre (0.303 calibre) machine gun to provide a minimal
At the time, Mitsubishi
was heavily committed to building other aircraft, and production of the
Ki-46-I was slow. Manufacturing problems were aggravated by the fact
that the Ki-46 had been designed for high performance, at the expense
of ease of manufacture and maintenance. A few were delivered for Army
evaluation during the spring of 1940, and in a short time a number of
them were provided to the Shimoshizu Rikugun Hikogakuko (Shimoshizu
Army Flying School) for crew training.
By the spring of 1941,
the Army had at least 386 Ki-46s on order, but they were still only
being delivered at the rate of four a month. Mitsubishi was ordered to
stop production of some older aircraft and shift resources to building
the Ki-46, and by November 1941 deliveries reached ten aircraft a
month. Monthly production would continue to increase, to a peak of 75
aircraft delivered in March 1944.
problems and weaknesses were uncovered as the Ki-46 was put into the
hands of operational pilots. Trials in Formosa revealed that engine
vapour lock was a considerable nuisance under hot and humid conditions.
The problem was fixed with a small change in the position of fuel lines
around the engine, and a change to higher octane fuel.
The main landing gear
also proved to be too weak, often collapsing on hard landings, which
were fairly common due to the Ki-46's high wing loading. Although some
minor fixes were implemented, the Ki-46 suffered from weak landing gear
all through its life. The Ki-46 also proved un-manoeuvrable and had a
sluggish rate of climb, partly due to a tendency for the oil to
overheat. However, the Ki-46 was not intended for air combat, and these
limitations were acceptable.
Some Ki-46-IIs were
fitted with a radio compass for long range navigation, with such
machines identifiable by a teardrop-shaped directional antenna on a
short pylon between the front and back cockpits. Later in the war, a
number of Ki-46-IIs were modified into three-seat radio navigation
trainers through the installation of a stepped-up secondary cockpit
behind the pilot's position. This variant was designated the "Ki-46-II
Kai", where "Kai" was short for "kaizen (improvement)".
* The new Ki-46
reconnaissance units engaged in probes of China and other areas that
the Japanese military hoped to seize in their plans for all-out war in
the Pacific. In October 1941, Ki-46s flew from Cambodia to survey
possible amphibious landing sites in Malaya.
When the war finally
broke out in December 1941, the Japanese offensive rolled over Western
colonial possessions in the Far East like a tidal wave. Within months,
the Japanese had seized Hong Kong, Malaya, Singapore, Burma, the
Philippines, and the Dutch East Indies. They established bases over the
western Pacific to protect their new empire.
The Ki-46 was a very
useful tool in their military operations. Operating from bases in Timor
in what had been the Dutch East Indies, the Ki-46 flew far over
northern Australia, and operating from bases in Burma the Ki-46 was
able to observe British naval activities in Ceylon, 1,600 kilometres
(1,000 miles) distant.
The Japanese Imperial
Army had shown unusual foresight in obtaining a specialized high-speed
reconnaissance aircraft, and the Imperial Japanese Navy, which wasn't
usually inclined to agree with the Imperial Japanese Army on anything,
recognized the merit of the Ki-46 to the extent of obtaining a small
number of the aircraft from the Army.
In the early stages of
the war in the Pacific, the Allies were reduced to improvising
vulnerable bombers and transports to the reconnaissance role. The
Ki-46, in contrast, could operate with impunity, since it was faster
than any fighters the Allies had in the region. Even when improved
Allied fighters became available, the Ki-46 proved difficult to catch.
The Allies quickly
recognized the Ki-46 as an impressive aircraft. In late 1942, they gave
it the codename "Dinah", and intelligence personnel described it as the
"Dinah with the nice linah!" The Germans were interested enough the
Ki-46 to consider obtaining a manufacturing license for it, but nothing
came of the exercise.
wingspan 48 feet 2 inches
wing area 344.5 sq_feet
length 36 feet 1 inch
height 12 feet 8 inches
empty weight 7,190 pounds
max loaded weight 12,790 pounds
maximum speed 375 MPH / 325 KT
service ceiling 35,170 feet
range 1,540 MI / 1.340 NMI