Today we’re taking a look at two Japanese bombers that were developed in the early 1930s:
the Mitsubishi Ki-1 & Ki-2.
In terms of appearance, they had that hallmark look of many bombers designed between 1925
and 1935, which was that of a corrugated box with wings.
Though they weren’t the most elegant of designs, these represented some of the company’s
first attempts at all-metal, monoplanes – with a couple of exceptions – though it must
be noted they were not completely developed by Mitsubishi, as they were both based on
an existing aircraft.
In February 1931 a Junkers K-37 was imported from Sweden and donated to the army by Domestic
sponsors as a ‘patriotic gift’.
This was part of an extensive program to financially stimulate the growth and development of aviation
technology within the country.
The K-37 was a Swedish built, militarised version of the prototype Junkers S-36, however
it had attracted little or no interest in Europe and so it was donated to Japan.
For 1931 the K37 was a fairly advanced design, featuring all-metal construction, two powerful
engines, strong cantilever wings, and a service ceiling of 7000m.
The Japanese Army Air force took interest and pressed into army service for examination,
in which it saw combat during the Japanese invasion of Manchuria in the latter half of
1931 Its performance impressed many in the Army
leadership, who in April of 1932 issued an exclusive specification to Mitsubishi for
the production of a new heavy bomber based on the Junkers K-37.
This was to replace the ageing Kawasaki Type 87, which was also based on a German design:
the famous Dornier Wal (val).
At around the same time as this, it was also decided to develop a light bomber based on
the K-37, which would become the Ki-2.
But for the sake of keeping things simple, we’ll look at the heavy bomber first.
Known in the army as the Type 93 Heavy bomber.
The specification called for a twin-engine monoplane bomber, with an engine power of
700hp each and the capacity to maintain flight on only one of these engines.
The bombload was to be 1 tonne, or 1 and a half on reduced fuel load, maximum speed at
3000 meters was to be above 240 kmh, and it was to have an operational altitude between
2000 and 4000 meters.
To meet these requirements, project manager Nobushiro Nakata proposed an enlarged version
of the K-37, using experience he had gained working on the gargantuan Ki-20 – a licence
built, military version of the Junkers G38.
The new bomber was thus 3.5 meters longer than the K-37 and its wingspan was 6 and a
half meters greater.
It was to have a crew of four: two pilots, a nose gunner / bomb aimer, and a rear gunner.
A Gosport speaking tube was used to communicate with the bomb aimer, though considering the
soundproofing of these earlier designs it should really be called a screaming tube.
Defensive armament consisted of three 7.7 mm machine guns, one mounted on a flexible
mount in the nose, another in the rear gunner’s station, and a third in a retractable ventral
position.
In keeping with the original design, it kept the old-school fixed landing gear, as a retractable
system was still considered far too complex and weighty for heavy bombers, that being
said it did feature two attempts at innovation.
It had a dispersed system of fuel tanks, rather than just one or two main tanks, so that if
one was hit, it would not affect the entire fuel system.
However, none of the tanks were self-sealing, nor were they armoured in any way…so this
system was probably useless as any hit to said fuel tanks would probably lead to the
eventual immolation of the crew.
The bomber also made use of Junkers ball-type joint connecters for the construction of the
wing and tail.
These were a feature on the original design, but not something really seen in Japanese
designs, and it allowed the aircraft to be broken down in sections for easier transport
by rail.
This was considered a particular advantage, as rail transport was logistically kinder
on fuel.
Following approval of a full-scale mockup, the first of two prototypes was complete by
March of 1933.
When it first flew, the prototype Ki-1 was a bit of a disappointment.
The planned 700hp Mitsubishi engines had suffered delays in development, and they were replaced
on the prototypes with 800hp Rolls-Royce Buzzards.
But despite the extra power, both prototypes were 20kmh slower than expected and their
handling was described as sluggish at best.
However, the Army didn’t really have any alternatives lined up that would be ready
within the next two years, and so the Type 93 Heavy Bomber was ordered into production
anyway.
It would later receive the designation of Ki-1 when the naming scheme was updated.
Unlike the prototypes, the production models were completed with Mitsubishi’s domestically
built engine: the water-cooled, 12-clyinder, Ha-2.
This put out 700hp and drove a wooden two-blade propeller.
In this configuration, the Ki-1s would begin to replace the old Type-87s during the course
of 1934, but the issue of performance had not yet been addressed, and with engines now
producing 100hp less than the prototype, problems quickly became apparent.
The bomber felt slow and heavy at the controls, and the engines -still in an unfinished state
of development- frequently delivered less than the required power, and the Ki-1 could
not maintain level flight under the power of one engine alone.
So not only did it look a bit like a brick, but it flew about as well as one too.
As a result of this, the 71st Ki-1 was taken from the production line for a series of modifications
to try and make the plane a bit more powerful and a bit less lethal.
An improved version of the Ha-2 engine was installed, which depending on what source
your look at either put out 720, 750 or 800+ hp…they all seem to conflict, which is wonderful.
These engines were mounted lower on the wing, which necessitated the lowering of the main
landing gear, and reduce drag this was now housed in a streamlined fairing that could
be removed on the ground for servicing.
Streamlining was key part of the improvements in general, with Mitsubishi hoping to improve
the Ki-1s woeful speed.
Some of the corrugated metal skin on the wings was replaced by smooth panelling, the pilot’s
canopy was extended rearwards to encompass the rear gunner position, and streamlined
fairings were used to partly enclose the externally carried bombs.
This modified version would be known as the Ki-1 model 2.
In total, 48 of these were produced, along with 70 of the first models, for a total production
run of 118 Ki-1s.
Though the model 2 was somewhat faster than the original, and it could now at least fly
under the power of just one engine, the Ki-1s reputation for being a slow, heavy, cumbersome
bomber lingered on, and it was not particularly well liked by its crews.
Its service life as a whole was relatively short.
This was partly due to its unpopularity, and partly due to its rapid obsolescence by the
development of the Ki 21 just a few years after the Ki-1 entered service.
It was not until 1938 that the Ki-1 would actually see combat.
As Japanese losses were beginning to mount in the war with China, Ki-1s were pressed
into frontline action.
Their results were highly mixed.
Thought some did manage to successfully bomb targets in a series of raids, many were either
destroyed on the ground or overwhelmed by fighters sent to intercept them.
The attrition rate rose rapidly, and after just a few months they were completely pulled
from combat duties.
The remaining Ki-1s would linger on as transports into 1939 and 1940, but none seemed to have
survived much beyond this.
Though the Ki-1 was deeply unpopular, the Ki-2 fared a bit better.
The design work was carried out by the same team that worked on the Ki-1.
Though it was nominally being built to replace the Kawasaki Type-88 light bomber, the Army
also wanted the Ki-2 to be capable of filling the roles of tactical reconnaissance, close
air support, and even potentially that of a heavy fighter, it being used to escort heavier
bombers.
Like the specification for the Ki-1, it also had to maintain level flight on one engine,
and an importance was placed on easy handling for night-time landings.
The design that was proposed was similar in dimension to the original Junkers K-37.
The wing and tail were essentially identical, with the exception of the ailerons, but the
fuselage was completely re-designed to meet the military requirements.
Said requirements called for a top speed of 260 km/h at 3000 meters, and a 4 and a half
hour flight endurance carrying a bombload of 500 kg.
The specification called for the bomber to be powered by a pair of 450hp Nakajima Kotobuki
radials, which were in essence a licence-built version of the Bristol Jupiter, but Mitsubishi
also submitted a proposal for the bomber to be powered by the Mitsubishi Type 94 Ha-8.
This was a 9-cylinder radial engine of approximately 500hp.
It was still under development, but the army was amenable to the idea once the engine was
proven to be reliable.
The prototype design that was submitted to the army had a crew of four, like the Ki-1.
But, unlike the Ki-1, its bombload was carried internally, the nose gunner position had a
new ball-style turret, and there was provision in the design submissions for the fixed landing
gear to be replaced with a retractable one.
However, the Army found the design of the turret and landing gear to be too innovative
for their current needs, and they were deferred for use until a real need arose.
And so, with an open gunner position, open cockpit, and a fixed landing gear, the prototype
Ki-2s were completed in the spring of 1933, and initially things looked good.
It performed reasonably well during the initial test flights and manufacturer trials.
Though its top speed fell short of requirements by 5kmh, its handling qualities were praised,
and unlike the Ki-1 it was considered easy to fly in general.
Unfortunately, during these trials one of the prototypes stalled during its approach
for landing.
It came down hard and the fuselage broke apart aft of the main wing, with the entire crew
being killed in the ensuing crash.
Following this, the design of the fuselage was altered to give it greater strength, and
with the other prototype surviving its trials the aircraft was ordered into production as
the Ki-2 model 1.
The model 1 was built until 1936, with 113 units being produced, until production was
halted for a major re-design to modernise the aircraft.
The design features that had been deemed “too innovate” in 1933 – the enclosed nose
turret and retractable landing gear – were now introduced, along with several other changes
– the Army apparently realising that innovations were a good idea.
The pilot’s cockpit was now enclosed under a canopy, 550Hp Type 94 engines were finally
installed, and some of the corrugated metal skin was replaced by smooth panels, much like
on the Ki-1.
Testing revealed these changes had increased the top speed by 30km/h, the handling had
further improved, and as a result the Ki-2 model 2 was ordered into immediate production,
with 61 being built between 1937 and 1938.
The Ki-2s were liked by their pilots and crews far more than the cumbersome Ki-1, however
they would also have a fairly uneventful service life.
Though the modifications had improved the Ki-2s performance, the model 2 had a production
run of less than one year as it was being made obsolete as a light bomber by the more
nimble, single engine Ki-30.
Most Ki-2s were deployed in northern China and Manchuria, but by the outbreak of full-scale
war with China they had mostly been withdrawn from service.
Some did remain, including 14 of the 12th Hiko Rentai, and their superior performance
over the Ki-1 gave them a greater chance of survivability in the earlier stages of the
war.
The Ki-2 saw more combat than the Ki-1, with at least two squadrons of Ki-2s taking an
active part in the battle of Xuzhou.
However, as the time went on, many of these Ki-2s were destroyed either on the ground
or in the air, and the remaining few were pulled from combat duties by the end of the
year.
The Ki-2s only real claim to fame was that it spawned a record-setting civilian aircraft.
The Asahi Shimbun newspaper ordered an unarmed version of the model 2 variant.
Named the Otori, or Phoenix, It was equipped with a new cockpit, dual controls, and its
fuel capacity was increased.
Between 1936 and 1939 it completed a series of long-distance flights, including a 9,300km
flight around China.
But aside from this offshoot, neither the Ki-1 or the Ki-2 would cover themselves in
glory.
When first conceived, their designs could have been considered modern, but as was the
case for many designs of the early 1930s, they were rapidly made obsolete.
By the time the Ki-1 was entering operational service, the prototype for the Ki-21 had already
flown.
This too was a product of Mitsubishi’s design team, and its high speed and sleek looks were
a testament to the rapid advances in aircraft design.
Unlike the Ki-1, this aircraft would see extensive service, being operated from 1938 all the
way through to 1945.
But the historyof the Ki-21 is a story for another day.
As always thank you all so much for watching, and a special thank you of course to the Patreons,
with a special shoutout to Kevin, Delliardo, Bane, FB, Christopher R, Tronathon, Erik Hindman,
and John Austin Jr for their support as wing commander tier patrons.
Thank you all so much, and I’ll catch you all next time.