Friday, May 15, 2020

Fake Japanese Super-heavies

In 1939, the Imperial Japanese Army suffered total strategic defeat at the hands of the Soviet Union surrounding the village of Nomonhan, in Manchoukuo. This had been Japan’s first significant deployment of armour against a modern army. Tank development in Imperial Japan was still in its initial stages by the time the border conflict at Nomonhan began.

Japan had constructed a series of fortifications in Manchuria and Central China under the supervision of the Continental Fortification Research Committee, a department under the Imperial Army. This committee oversaw all major defenses in the region against the Soviet Union and Chinese warlords. Shortly after the Nomonhan Incident, the committee submitted an idea to construct special purpose tanks that were capable of breaking through heavily defended Soviet lines and force the Soviet armies back out of taken Manchurian lands. 

Historical Background

Colonel Hideo Iwakuro, an officer in the Military Affairs Bureau Tank Research Team, took an interest in the concept of a super-heavy tank capable of pushing through Soviet defensive lines, unmatched in firepower and armour. Japan built and tested an array of multi turreted heavy tanks from 1925 to 1938 in an attempt to implement a breakthrough vehicle. However, these tanks all had the same underlying issues: their armour was too thin to protect against anti-tank guns, and their armaments were inadequate. Due to weak engines, these prototypes lacked sufficient speed and mobility. But due to the large size of these engines, they forced the chassis to be larger. 

In the early months of 1940, Colonel Iwakuro along with a team of twenty engineers from the 4th Technical Research Group designed the superheavy tank at their headquarters in the Tokyo area. The superheavy tank project proceeded under the temporary name Mi-To (later, O-I). Construction work would be performed by the Sagami Army Arsenal in secret. As was customary with Japanese heavy tanks, the Mi-To had a multi turreted layout with two auxiliary turrets in the front part of the chassis, one primary turret in the center of the hull, and a machine gun turret located at the rear of the chassis. The tank design was heavier and larger than any other tank of its time. Basic in its shape, the vehicle kept a box-like appearance for ease of manufacturing and assembly of its plating.

Technical drawing document of the O-I super-heavy tank. One of various drawings purchased by Finemolds in 2014. (Source: author's collection)

The tank was sent to the Sagami arsenal for military trials upon completion of the prototype. Here, the tank was renamed the O-I. Due to faulty performance of the engine and the unsustainable weight of the tank, trials were concluded as a failure. The vehicle was then kept in a state of disrepair for the duration of the war. Upon the surrender of Japan, the records and materials of the project were kept privately near Sagami. Thought to have been destroyed after the war, for decades the vehicle was shrouded in mystery. Official documented records of the vehicle and plan were minimal in the remaining archives of Japan. Only through the writing of Tomio Hara, the head tank developer for Japan during the war, had the tank been mentioned in detail. However, in 2014, President Kunihiro Suzuki of FineMolds corporation purchased the remainder of the O-I’s documented reports from their holding place at Wakashishi Shrine in Fujinomiya. These were under ownership of Wakashishi Shrine museum staff. Along with the tank's reports, the last remaining physical piece of the vehicle, a track link of the prototype, also remained at Wakashishi Shrine on display.

Kunihiro Suzuki officially revealed and published these findings in the summer of 2015. Prior to this, information on the vehicle remained subject to great skepticism. Authors of various books and other media interpreted the tank in their own artistic licensing. Because of this, many false versions of the tank exist. Some of these interpretations have been regarded as separate projects, or the real accounts of the tank and its history.

Fake Iwakuro 100 ton  
(Commonly called O-Ni, or Type100 O-I, or O-I 100 ton)

Popularized by the Japanese book Tank and Tank Battles (2012), the Iwakuro 100 ton tank was described as the first super-heavy tank built by Japan. This publication contained extensive information detailing the development of Japan's tank projects. Mitsubishi engineers that took part in development were gathered and interviewed for information. One of these workers, Shigeo Otaka, described the O-I prototype and the information gathered from mobility tests conducted in late 1942. This corresponded with his accurate sketches of the tank.

Otaka recalls the vehicle as weighing 100 tons, significantly heavier than any other vehicle the Japanese army had employed. Development of the project had been under the supervision of Colonel Hideo Iwakuro in 1939. Iwakuro sought to develop a new breakthrough tank heavier than any other vehicles. This super-heavy tank was written to be as long as 10 meters, significantly longer than tanks of other nations. The tank’s height and width were listed as 4 meters.

Artistic interpretation of the O-I called the 100 ton tank. (Source;戦車と戦車戦 2012年)

In the book it is mentioned that the vehicle’s armament consisted of two 47 millimeter guns, a single 105 millimeter cannon, and two to three machine guns. The publication’s artistic reference pictured the Iwakuro 100 ton as a long yet thin super-heavy tank with conically designed turrets. The hull of the drawn tank depicted a single-step body with a recess in the front to accommodate two auxiliary turrets housing the 47 millimeter guns. Based on the artistic drawings, some depictions of this vehicle illustrate machine guns placed on the front central hull, but others do not have these present.

Artistic interpretation of the O-I
 called the 100 ton tank. (Source;戦車と戦車戦 2012年)
In the summer of 2015, the video game company Wargaming Limited introduced the Japanese 100 ton O-I under the name “O-Ni”. This vehicle matched visual appearance and statistics to that of the 100 ton’s book counterpart. The name of the vehicle should be noted, as it does not match the Japanese Iroha naming classification system. The Japanese military organized vehicles by two categories; class and the number of the class to be introduced. The O-I had been the first super-heavy tank Japan built. Because of this, the tank received the designation O (meaning super-heavy), and the letter I (representative of 1). The O-Ni under this system would translate to Super-heavy two. While this would be accurate naming of the tank, because it is a misinterpretation of the historical vehicle, no such tank would have existed.

Historical Context

The O-I consisted of a 4 turret format on a two-step hull.  Two auxiliary turrets were coupled in the front of the hull. These turrets were constructed to carry Type1 47 millimeter tank guns. The Type1 entered service in 1941 as the standard anti-tank cannon for the army. The purpose of these anti tank turrets was to engage enemy vehicles, such as armoured tanks. One central turret stationed in the upper step of the tank was present. Initial drafts of the vehicle requested for this turret to have been armed with the army’s Type96 150 millimeter howitzer. This was to be prioritized for use against armoured fortifications. The fourth turret had been placed on the aft end of the tank. This turret had been armed with two 7.7 tank machine guns. These were intended to provide vehicle defense from enemy engagements to the vehicle’s flank.  

Drawings of Engineer Shigeo Otaka of his
memory of the O-I.  (Source;戦車と戦車戦 2012年)
The proportions of the O-I tank had been a matter of concern for the Mitsubishi engineers that took part in the vehicle’s development. The proportions of the vehicle were documented at a width of 4.84 meters , height of 3.63 meters, and length of 10.120 meters. Due to the size of the tank, significant amounts of steel were required for construction. With the vehicle being privately funded through an embezzlement scheme, delays due to lack of funding were frequent and costly to the tank’s assembly. Throughout development, the decision to cancel the project was considered on multiple occasions. 

The weight of the O-I at the date of its mobility testing in 1943 was 96 tons. This weight accounted for only the unarmoured chassis, compared to the designed gross weight of 150 tons total. Construction complications resulted in a point of delay, halting further assembly of the prototype. Mitsubishi documents the weight of the prototype vehicle in a structured list. Unaccounted in this listing had been that of the central turret. Due to the resources required to construct the armoured turret, a temporary wooden scaled replacement had been made on June 4th 1942. Fitted to the prototype on July 10th, the 96 ton prototype was then ready for mobility tests and inspection by ranking army officials.

Description of the tank's armour plating by Finemolds.
 日本の重戦車 (2016年) 
According to Shigeo Otaka in the interview, the O-I had been assembled with mild tempered steel plating. Upon complete assembly of the body, armour plating of 75 millimeters replaced various sections of the tank’s front and aft panels. Additional armoured plating of 75 millimeters were to be added onto the tank’s body by bolting them to the underlying armour plating. The vehicle sides were replaced with 35 millimeter armoured steel plating with an additional 35 millimeter skirting layer bolted on top of the hull. Flooring of the prototype was constructed using a three staged plate assembly to reinforce the vehicle.

Transportation of the tank had been a key requirement in the development of the O-I. Due to the excessive weight of the vehicle, transportation via army railways became impossible. Separate transportation of various components at a time was required. Modular armour plating had been requested early in the vehicle’s development to make the practicality of the vehicle effective on the frontline. On May 26th, 1943, disassembly of the O-I had begun for transportation to the Sagami Arsenal outside Tokyo. The tank was disassembled and transported by June 9th. Assembly took place from July 1st to the 20th, after which it was to be subjected to official army trials.

3D model of 1/72 scale of the O-I tank. Produced by Finemolds using documentation obtained by its president in 2014.
 ( Finemolds)

Fake 120 ton O-I   
(Commonly called O-Ho, or Type120 O-I)

The first representation of this interpretation comes from the book series Japanese Fighting Vehicles of WW2, written by Yusaku Shimada. The book describes the 120 ton O-I as a tank project starting development in 1944, after the failed trials of the 100 ton tank. It was said to be a secret project, sent to Manchoukuo upon completion and used against the Soviet army in 1945. The vehicle is written to have been designed with aid of Nazi Germany by an exchange of super-heavy plans to Japan. The tank is often described as well protected by armour plating ranging from 200 millimeters to 300 millimeters.

Artistic interpretation of the 120 ton O-I. (Source; 帝国陸軍陸戦兵器ガイド 1997年)

Illustrated in Japanese Fighting Vehicles of WW2, the 120 ton is designed with a two-step hull, mounting two auxiliary turrets and a primary central turret. Both auxiliary turrets were mounted on the upper step of the tank’s body, each mounting 47 millimeter guns. One was positioned to the front, with the second to the aft of the tank. The primary turret housed a 105 millimeter gun coupled with machine guns. The forward lower step of the tank is drawn in similar fashion to standard Japanese vehicles such as the Type97 Chi-Ha and Type3 Chi-Nu medium tanks. This bottom step was designed to house the front transmission of the vehicle. Machine guns are spread out around the tank, such as in the rear central turret and front hull of the tank.
Artistic interpretation of the 120 ton O-I.
(Source; 帝国陸軍陸戦兵器ガイド 1997年)

A second drawing of the tank had three turrets again but in a different format. There were two auxiliary turrets; one mounting a 47 millimeter gun, and the other a machine gun. In the case of this interpretation, bulges were made on the upper step of the hull to accommodate an auxiliary turret crew. While the cannon is mentioned as the 105 millimeter gun, the drawing illustrates the Japanese Type5 75mm tank gun serviced with tanks such as the Type4 Chi-To and Type5 Chi-Ri. Other depictions instead show the 120 ton tank with the experimental high velocity 105 millimeter tank gun. The tank is written to have been built by late 1944, weighing 140 tons total.

Rumours claimed that only the turret of this vehicle was transported to Manchuria. This rumour erupted due to photography of Soviet soldiers in Manchoukuo standing in front of a bunker with a steel turret.

In the summer of 2015, the video game company Wargaming Limited introduced the Japanese 120 ton O-I under the name “O-Ho”. This vehicle matched visual appearance and statistics to that of the 120 ton’s book counterpart. The name of the vehicle should be noted, as it does not match the Japanese Iroha naming classification system. The Japanese military organized vehicles by two categories; class and the number of the class to be introduced. The O-I had been the first super-heavy tank Japan built. Because of this, the tank received the designation O (Meaning super-heavy), and the letter I (representative of 1). The O-Ho under this system would translate to Super-heavy five. The reason for this mistake is not clarified. However because the tank is a misinterpretation of the historical vehicle, no such tank would have existed.

Both O-Ho and O-I published by the video game company Wargaming Limited. It can be seen the visual difference between
the 120 ton tank artistic interpretation and the correct model of the O-I tank that had been designed and built. (

Historical Context

The claims of the 120 ton O-I generally originates from the words of Tomio Hara in his book, Japanese Tanks (1978).  In this book, Tomio Hara briefly writes on the history of the O-I tank along with the specifications of the prototype and project. Upon failed prototype trials conducted in 1943, the Japanese army attempted to fix the damages and underlying issues. By 1944, a proposal had been made to make alterations of the tank and rebuild the prototype. These changes, however, did not happen. The Army ended up disbanding the program due to the need for such a tank no longer existing.

The construction of the suspension, hull and secondary turrets of the Mi-To finished in early 1943. The chassis weighed 47 tons empty without additional armour. The tank weighed 97 tons when configured for mobility and defensive tests, but this did not include the weight of the turrets. The Mi-To weighed 120 tonnes when the three auxiliary turrets and other pieces of armour plating were installed. The primary turret and additional 75mm plating would have given the tank a weight of 150 tonnes, as the original design intended. 

Interior module placement of the O-I tank. It can be seen here the 4 turret placement in its correct figuration. One of various drawings purchased by Finemolds in 2014. (Source: author's collection)

Removed parts were transported by truck to the Sagami Arsenal. All parts were covered by a wooden box at the rear of the trucks to hide components, and prevent citizens or potential spies from discovering the super heavy project. The main hull was placed on a 30 ton trailer, and towed by a 13 ton tracked towing tractor. The turrets were towed by Type 95 Ha-Go light tanks and a Type 97 Chi-Ha. Moving all the parts from Mitsubishi’s construction center to the arsenal took 19 hours. The tank was not completely disassembled until June 9th. Once at Sagami, re-assembly began on July 1st. Once completed on the 20th, the trials were scheduled to begin on the 1st of August.

Weight distribution of the prototype.
(Source: author's collection)
On the day of the trial, high ranking officials in the Army were present to witness the first Japanese superheavy tank in motion. The Mi-To received a name change to O-I to follow Japanese naming convention that was standard. Tomio Hara, head of the Sagami Army Arsenal, was also present for the trials. 

Conditions for the trial were poor. Weather during the previous days caused the soil to soften, and the terrain became uneasy. The road at the proving grounds was narrow, and when the O-I began moving down the road, the tank started to drift. This damaged the roadwork, resulting in the tank sliding off the road and into the soil. A change in the trial’s planning focused on the O-I traversing around in the dirt next to the facility it was kept in. Due to the surrounding buildings, its top speed could not be showcased, and traversing was difficult. The weight of the vehicle caused the land to start sinking in during pivots. The O-I reached the first three gears in its mobility test. At the end of the first day of the trials, the O-I had been put back into its garage, and the engineers noticed that the seventh lower track roller’s bearing was damaged, and it was caught between the drive sprocket and the outer plate skirt. The outer plate had broken through, and the gear of the drive sprocket broke apart into two pieces.  The wheels were of cast construction and lacked rubber lining. During movement, the O-I chassis experienced severe rocking motions. Heavy duty shock absorber assemblies were placed inside the vehicle. The top and bottom of each shock absorber’s spring were connected to the suspension by two arms extending from the front and rear.

Engineer's notebook pages documenting the events of the O-I's mobility testing. The engineer's notebook was part of the collective notebooks documenting the O-I's development history. These were purchased in 2014 by Finemolds.
(Source;日本の重戦車 2016年)  

From August 3 to August 8, the engineers began repairing the damage that had been done to the tank. 32 of the total 64 bearings were broken during the tests due to the bearings having insufficient strength. The excessive weight of the O-I caused the entire right side of the tank to collapse when at an extreme angle. Engineer Shigeo Otaka recalls the O-I undergoing immediate repairs to continue its trials. However, due to the steep cost of the repairs, they were put on hold for over a year, and the tank stayed at Sagami Arsenal until March of 1945. The war was nearing its end, and the usefulness of the O-I in Manchuria began to fade. The Soviet Union was no longer Japan’s primary enemy, and the development of more powerful anti-tank guns by the Soviet Union made the armour protection of the superheavy tank obsolete. The project to build a single prototype unit came at a steeper expense than originally thought possible, and mass production was not realistically possible for Japan during wartime. The project was thus deemed a failure.

Fake Type4 / Type5 Superheavies

In the summer of 2015, the video game company Wargaming Limited introduced the Japanese super heavy tanks to their game. Of these vehicles, two tanks that had been added were called the Type4 and Type5. These super heavy tanks represented Japan’s final experimental super heavy tanks of the war. According to Wargaming Limited, the tank’s histories were described as follows:

"This is it. The top of the Japanese super heavy tank line. The Japanese Maus. The Type 5 Heavy was designed to defend coastal positions and to break through the enemy’s defences, which is reflected in the characteristics of this behemoth. " -

"The Type 5, also known as the Type 2605, was one of the variants of the O-I superheavy tank, developed during WWII. The vehicle was planned to be used for breaking through fortified enemy lines and for coastal defense." -

Both Type4 and Type5 published by the video game company Wargaming Limited. (

Supposedly, the Japanese decided to procure more super heavy tanks after the failure of the O-I’s development. The intentions of these new tanks were described as attempts at coastal defenses against Soviet invasions. By 1945, the Japanese army resorted solely to the defense of the home islands and remaining territory. However according to Wargaming Limited, these tanks were aimed for offensive operations.

The company released documented Soviet reports on captured Japanese super-heavy project plans in late 2013. These materials claimed to have been procured by a Soviet engineer by the name of Grigoriev belonging to an engineering division. A report on the findings were documented in a Soviet written report titled “Cooling of Japanese heavy tank projects”. In the file, it is claimed that two new super-heavy tanks were designed with intentions of mounting German BMW 12 cylinder engines, as opposed to the O-I’s Kawasaki 550 horsepower (rated to 600) engines. Further details were reported of advanced ventilation systems used on the tank design. A second variant of the tank existed with a 35% size reduced engine bay. The vehicles were claimed to have weighed over 200 tons. The engineer claims to have seen a wooden mockup of the vehicles in Manchoukuo with experimental engines. During the Soviet invasion, findings of the built turret of these tanks existed, with naval guns mounted for coastal defense.

Supposed technical drawing by Soviet engineers in 1945 detailing the cooling system of the Type5 heavy tank. These were
presented by Wargaming in 2013, showing no source material suggesting the authenticity of the claims.

Historical Context

The authenticity of these Soviet documents comes into question due to various errors in their claims. After the failed testing of the O-I prototype in 1943, the Army expressed concerns regarding the usefulness of the vehicle, considering the war’s deteriorating condition. A brief proposal at revising the tank’s mechanical issues had been proposed in 1944, however, this was quickly denied. After this, the Japanese army focused solely on tank projects aimed at the defense of the home islands against allied invasions. Super-heavy tank concepts were not pursued and forgotten with the O-I’s cancellation.

Questions as to how the Soviet military obtained information on private tank projects conducted in Japan leaves skepticism. Research and development of tanks existed solely in arsenals in Honshu, not outside the home islands inside Manchoukuo. Documents regarding the tanks cooling system do not exist inside Japan’s national archives. It is unlikely that they would be conveniently placed in the area of the Soviet invasion of Manchoukuo to obtain. 

Photograph of two Soviet soldiers infront of a captured Japanese fortification in 1945. Location of the photograph is Koto fortress on the coast of Manchoukuo. The turret has been claimed to have been that of the O-I/Type4 and 5 heavies. However this has not been proven. (

Commonly discussed is a photograph from the Soviet invasion of Manchoukuo in 1945, showing Soviet soldiers posting for a photograph in front of a captured Japanese bunker defense. This bunker mounted a large steel turret equipped with a 140 millimeter coastal naval gun. The photograph is taken at the Japanese fortress of Koto on the Manchurian coastline. Soviet forces captured the fortress containing one of the last remaining Japanese holdouts in the region. Various coastal defense turrets were positioned at Koto fortress for the invasion. These turrets consisted of thinly armoured, housed naval batteries alongside the Manchurian coastline. While the turret photographed is likely to have been real, it is also likely that it belonged to no such tank project. The Imperial Japanese army would not have used Japanese naval guns in their vehicles. Due to standards and regulations, only army equipment was permitted to be used within the army. 


- 第8編  技術関係事項Ref. C15120358000
- 日本の戦車 (1978年) 
- 日本の重戦車 (2016年) 
- 日本陸軍の火砲 (2012年)
- 戦車と戦車戦 (2012年)
- 帝国陸軍陸戦兵器ガイド (1997年)
- 日本陸軍超重戦車 株式会社学研プラス (2016年)


  1. Very interesting article, thanks for your work !

  2. one thing to notice is that the artist, who probably had no engineering background, recreated those description by thinking «tanks looked like this back then, I guess they would keep the overall design» because it is clear that first drawing (Iwakuro) is clearly influenced by the Chi-Ha and Types 91 and 95
    the exhaust on the side, the turret shape, the engine deck being sloped towards the rear, etc
    the 120 ton drawing as some Chi-To/Chi-Ri feel mixed on a closer despiction of the real O-I

  3. Hello Mai. What's your thoughts on what the Type 5 turret picture could be? Also, how did Chi-Ri production go?