Imperial Japanese Army Super Heavy Tank 150 ton (O-I), this 1/72-scale kit was released by FineMolds in 2015. Model by Nuno Lima.
The O-I (Oi-sensha) was a super-heavy tank prototype
designed by the Imperial Japanese Army during the Second Sino-Japanese War
after the Battles of Nomonhan in 1939. The O-I is one of the Second World War’s
more secretive tank projects, with documentation regarding the tank being kept
private for over 75 years at Wakajishi Shrine, Fujinomiya. Surviving files have
been purchased by FineMolds Inc., and publicly previewed in mid-2015. The
multi-turreted 150-ton tank was designed for use on the Manchurian plains as a
supportive pillbox for the Imperial Japanese against the Soviet Union. The
project was disbanded four years after the initial development began, deemed
unsatisfactory for continuation in 1943 after the lack of resource material for
the prototype.
History and development
After 1939, the Imperial Japanese Army quickly came to
realize that previous forms of mechanized warfare were proved inefficient after
their defeat at Khalkhin Gol.
Development of the super-heavy project was spearheaded by
Colonel Hideo Iwakuro, the head of the Ministry of War of Japan (Rikugun-shō).
Iwakuro opposed Japan’s advances towards the Soviet Union in 1939, and with the
Japanese defeat, he decided to initiate a project to construct a heavily
armored tank capable of withstanding large-caliber field cannons. Iwakuro
assigned Colonel Murata of the 4th Technical Research Group to design and
construct the super heavy tank in 1939. Colonel Murata noted Iwakuro’s words as
described;
“I want a huge
tank built which can be used as a mobile pillbox in the wide open plains of
Manchuria. Top secret.”
“Make the
dimensions twice that of today’s tanks.”
The 4th Technical Research Group began designing the
super-heavy vehicle throughout 1940, attempting to meet Colonel Iwakuro’s vague
instructions on the ultimate goal of the project. By March 1941, the research
group had finished initial tank design and was ready to begin construction. The
following month, a group of pre-selected engineers were chosen to partake in
the building of the super-heavy tank. One recorded engineer was Shigeo Otaka,
who stated they were sent to the 4th Technical Research Group’s previous
headquarters in Tokyo. There, they were guided through a barracks containing
multiple small fitting rooms, where they were to conduct meetings and reports
on the progress of construction of the super-heavy vehicle. Towards the end of
the barracks facility was a fully-enclosed room devoid of windows, with
soundproofed walls to prevent external personnel from overhearing discussions
related to the project. Each officer present possessed a portion of the
project’s blueprint, which, when assembled, projected the full design of the
tank, labeled “Mi-To”. The name originated from a collection of the
Mitsubishi industry and the city, Tokyo; given to the vehicle to uphold secrecy
of the tank’s project.
The chosen engineers voiced their concerns regarding the
Mi-To’s design noting that previously, the largest-sized Japanese tank had been
the prototype Type 95 Heavy in 1934. Issues that had been noted with heavy tank
experiments in the years preceding the Mi-To showing Japan’s generally
unsuccessful testing on multi-turreted vehicles exceeding the weight of
standard armored vehicles. However, with the threat of a second Russo-Japanese
conflict becoming more apparent, the project continued despite the engineer’s
doubts on the size and mobility of the vehicle.
On April 14th 1941, the engineers began the construction of
the Mi-To under secretive means. This entailed privately-made mechanical parts
and equipment being shipped to the construction zone. Colonel Murata’s original
concept was to complete the super-heavy tank three months after the initiation
of Mi-To’s construction. This, ultimately, did not come into fruition; as
technical issues on the project began to arise. Due to the limitation on
material consumption by the government, the amount of parts that could be
secretly shipped-in began to dwindle. By the first month of construction,
essential construction resources had been depleted and the issues with the
vehicle’s cooling system further caused delays. The construction of the Mi-To
was postponed until January 1942, a delay of nine months.
After the Mi-To’s construction was resumed, the hull was
completed on February 8th 1942. The tank had reached near-completion and was
being prepared for mobility testing. Mitsubishi built the four turrets for the
tank in May of the same year. Initial assembly of the tank’s armament took
place soon after the turret’s superstructures were completed. However; the
project once again did not have the necessary resources needed for the few
remaining parts required for the final assessment. Due to this, the primary
turret was removed as it lacked a 35-millimeter-thick roof plate, which had not
yet arrived. Thus, the project was put on standby, until further development
could continue. The total weight of the vehicle at the time was 96 tons, due to
the lack of remaining structural plates and absent 75mm bolted-on armor.
The date on which the construction of the tank resumed is
unknown, although active testing of the tank was scheduled for late 1943. The
tank was unveiled to the Imperial Japanese Army’s highest command in 1943, and
received a name change to O-I. This followed Japanese naming convention (O
translating to Heavy, I for First, making it “First Heavy”) that was
standard. In his place was Lieutenant Colonel Nakano, Murata’s assistant and
colleague. Tomio Hara, head of the Sagamia Army Arsenal, was also present.
Following the demonstration, senior officials within the IJA requested that
field trials begin in August of the same year. The tank was disassembled at
2:00 AM one night in June of 1943 and sent to the Sagami Army Arsenal in
Sagamihara, 51 kilometers from Tokyo. The vehicle arrived at the depot in June,
and was reassembled and tested on the 1st of August.
On the day of the trials, the O-I performed satisfactorily
until the second hour of the tests. While maneuvering on off-road terrain, the
tank sank into the ground by up to a meter; attempts at traversing the hull to
extricate the vehicle proved fruitless, resulting in further sinking due to the
vehicle’s suspension coils compressing. The tank was eventually towed out, and
further testing was continued on concrete. However, the earlier damage to the
suspension resulted in vehicle’s movement damaging the concrete, which in turn,
further damaged the suspension bogies to the point that further testing could
not continue. The trials were postponed, and later canceled the following day.
Nevertheless, the trials conducted at the testing field were
considered to be a success, and the vehicle was deemed ready for use in spite
of its flaws. The engineers began disassembly of the tank on the 3rd of August
due to resources being limited and the inability to maintain the tank in the
field. Disassembly of the tank was completed on August 8th. Two days later, the
engineers noted in a log that they were to inspect the parts and conduct
research to fix the issues the O-I would face.
The fate of the O-I after its field-trials which took place
on the 1st of August is unclear. Russian reports claim the Japanese were in
possession of a wooden O-I mock-up mounting a Daimler-Benz DB 601A engine in
1945, however other sources point to the scrapping of the remaining parts of
the same year. The remains of the O-I reside at the Wakajishi Shrine, with a
track link of the prototype still present.
Design
The O-I was conceived out of the necessity to produce an
armored vehicle capable of withstanding modern weaponry being able to return
fire with similar firepower. The O-I was designed to act as a mobile pillbox,
supporting infantry and mechanized groups along the border of the Soviet Union.
The tank had a length of 10.1 meters, width of 4.8 meters, and a height of 3.6
meters. The dimensions of the vehicle closely matched those of the Panzer VIII
Maus. The tank was envisioned to have a standard thickness of 150 millimeters
front and rear, in order to protect against common anti-tank weapons of the
time, yet it was constructed with armor 75 millimeters thick. However, an
additional armor plate could be bolted on to bring the total thickness of the
armor to 150 millimeters. The use of additional armor allowed for ease of
construction and transportation, while also providing the tank with additional
defense. Side armor on the hull superstructure was 70 millimeters thick. The
additional armor plates were 35 millimeters thick, but armor surrounding the
suspension was only 35 millimeters thick. This made the tank’s theoretical
armor on the side 75 millimeters. There were eight wheel-supporting beams
located on both sides of the suspension area which added an additional 40
millimeters of armor to specific locations on the side of the O-I. 40 ladder
pieces were placed around the tank to provide crew with the ability to climb
onto of the vehicle with ease.
The two 47mm cannons used in the two frontal turrets were
also modified to fit the armor layout of the tank. The weapon’s barrels were
reinforced with steel to secure them to the tank, due to the standard gun not
adequately fitting into the turret.
The tank was both designed and built with two inner armor
plates to divide the interior into three sections; walls with two doors each
and an ultimate thickness of 20mm. This allowed the crew and modules to remain
relatively safe while the structure was kept safe with supporting stands. These
supports allowed the interior armor plates to stay stable and also prevented
collapse. Inside the O-I were two Kawasaki V-12 engines, both located in the
rear, parallel lengthwise, to give room for the rear turret operator and
transmission. The transmission copied that of the Type97 Chi-Ha’s, but used
larger parts and gears making the total weight heavier. The vehicle had a coil
spring system, with eight 2 wheeled boggies, totaling 16 individual wheels.
Data Sheet
General
Name: O-I
Factory: Private – Mitsubishi
Units Produced: 1
Type: Super Heavy Tank
Year Built: February 8th 1942
Length: 10.1 m
Width: 4.8 m
Hull Width: 4833 mm
Height Full: 3.6 m
Turret height: 1065 mm
Track width: 800 mm
Track Pitch: 300 mm
Track Thickness: 58 mm Half, 108 mm Full
Total Weight: 150t (96t prototype)
Engine
Name: Type 98 V12 Kawasaki
Power: 550hp (1100hp total with second engine)
Weight: 1020kg
Gears: 6
Lubricant type: Oil
Maximum speed: 40kmh on road (prototype), 29.4 kmh (design)
on road
Hull
Hull height: 2530 mm
Hull Width: 4833 mm
Upper Front Plate: 150mm @ 56,29°
Lower Front Plate: 150mm @ 45°
Lowest Front Plate: 70mm @ 70,5°
Side plate: 35mm @ 0° + Bolted 35mm @ 0°
Superstructure side plate: 75mm @ 0°
Upper Rear Plate: 150mm @ 18°
Lower Rear Plate: 150mm @ 33,01°
Lowest Rear Plate: 30mm @ 75,99°
Top plate: 50mm @ 0°
Bottom plate thickness: 30mm @ 0°
Turret Primary
Turret height: 1065 mm
Turret side faces: 150mm @ 90°
Turret top: 50mm @ 0°
Turret Ring: 1870 mm
Armament
Model: Type96 15cm Howtizer
Weight: 4,140 kg
Elevation: -5 ° to + 20 °
Amount of ammunition: 100+
Type of ammunition: Type 95 APHE, Type92 Spifire HE, 4th
Year HEAT
Ammunition Types
Name: Type 95 APHE
Shell weight: 36000g
Velocity: 540m/s
Penetration: 125mm @ 230m, 120mm @ 510m, 112mm @ 755m, 102mm
@ 1000m
Explosives: 6150g
Name: Type 92 Spifire HE
Shell weight: 36000g
Velocity: 540m/s
Explosives: 6150g
Name: 4th Year HEAT
Shell weight: 21040g
Velocity: 650m/s
Explosives: 6150g
Secondary Armament
Model: Type1 47mm Experimental
Weight: 600(+/-) kg
Elevation: -10 ° to + 20 °
Amount of ammunition: 100+
Type of ammunition: Type 1 APHE, Tungsten Alloy Toku Kou
Prototype
Name: Type 1 APHE
Velocity: 810m/s
Penetration: 65mm @ 200m, 65mm @ 500m, 50mm @ 1000m, 45mm @
1500m
Explosives: 17g
Name: Tungsten Alloy Toku Kou Prototype
Velocity: 810m/s
Penetration: 85mm @ 0m, 79mm @ 200m, 70mm @ 500m, 56mm @
1000m, 45mm @ 1500m
Explosives: 17g
