Light / Medium Tank Type 89 (Type 89 Medium Tank I-Go)

Introduction
Average танк The Type 89 I-Go is probably the most discussed tank by the name of the tank itself and its modifications. There are several Western versions of the names of the tank and its modifications. In Japan, there are also two versions now. I don’t know when the old version appeared, and the new version became known at the beginning of the 21st century. It appeared on Takizawa’s website somewhere around 2015, and later on other websites. Below is written about the different versions, including the new Japanese version about the modifications of the Type 89 tank.
A bit of history
The Imperial Japanese Army quickly recognized the potential of tanks and began negotiations to purchase foreign reference models as early as 1917. On October 24, 1918, less than a month before the end of World War I, a heavy British tank, the Tank Mark IV (Female), arrived in the Japanese port of Yokohama, destined for the infantry school in Chiba Prefecture. Subsequently, 13 (in Japan it is believed that 22) Renault FT (Tank Renault type A, better known as "Ko" Gata Sensya), and four Mk A Whippets were also delivered in 1919, but were not given a local designation.
In 1929, Japan was forced to buy new tanks from abroad while its own production was just getting going, 10 (in Japan they think it was 23) Renault NC-27 tanks (Tank "Renault" type B, better known as "Otsu" Gata Sensha), and in 1930 two Carden-Loyd Mk.VI tankettes (Type "Ka" Kijusha), and 4 more were bought later. And this is not counting the 1-2 units bought abroad for testing.
Since 1925, the construction of tank forces began. On May 1, 1925, the 1st Tank Corps was formed in Kurume, Fukuoka Prefecture, and the Tank Corps of the Infantry School in Chiba. Four heavy (medium) British Mk A Whippets and six light French "Ko" Gata Sensha ("Renault" A) were transferred to service. Almost all the tanks that the Japanese army had at that time. In the late 20s, the cavalry also wanted tanks and subsequently built them in series, a total of three models, essentially tankettes (Type 92, Type 94 TK, Type 97). Vehicles built to support the cavalry were called armored cars (装甲車 - Sokosha), and those built to support the infantry were called tanks (combat vehicles) (Sensha - 戦車).
In 1925, the Japanese army introduced a new classification of tanks: light, with a combat weight of less than 10 tons (Renault FT), and over - heavy (Mk A Whippet). The first Japanese multi-turret experimental tank built, "Experimental Tank No. 1" (試製一号戦車), as well as all subsequent experimental tanks weighing more than 10 tons, are classified as heavy according to this classification. Light tanks were to form the basis of Japan's tank forces, and heavy tanks were to support them. But the Japanese industry was never able to master the production of heavy tanks.
The first heavy tank created to support the Type 89 light tank was the Type 91, an experimental heavy tank built in a single copy. The second heavy tank was the Type 95, also known as the "Ro-Go", which means "Second". Four tanks were built, and then production ceased. Intelligence reports from some countries, including the USSR, mention another heavy tank, the Type 4. There is no reliable information about subsequent heavy tanks, only drawings or mentions that they existed.
In 1935, the Imperial Japanese Army introduced a new classification of tanks: those with a combat weight of less than 10 tons were called light, those with a combat weight of 10 to 20 tons were called medium, and those with a combat weight of more than 20 tons were called heavy. The Type 89 I-Go was first replaced by the new Type 95 light tank, called the Ha-Go (translated as the Third), and then by the new medium tank, the Type 97, better known as the Ti-Ha. I wonder if the Ha-Go tank was renamed the Ke-Ha after switching to the Iroha system? The names of the tank, Kyu-Go (nine-five) and Ke-Go (light fifth), are incorrect.

Name of the tank
In late 1929, the prototype was standardized as the Type 89 light tank (八九式軽戦車, hachikyū shiki kesensha, meaning Type 89 light tank). It was also given the codename "I-Go" (イ号車, shortened to "First" (イ号)). This designation remained in effect until September 13, 1935, when it was reclassified as the Type 89 medium tank (八九式中戦車, hachikyū shiki chūsensha, meaning Type 89 medium tank), the Western designation for the Type 89 medium tank I-Go.
Since two versions of the tank with different types of engines were produced since 1935, they became known as the Type 89A Medium Tank (八九式中戦車甲型) or Type "Ko" (Type "A" - Gata "Kō"), the Western name is Type 89A I-Go Kō, and the Type 89B Medium Tank (八九式中戦車乙型) or Type "Otsu" (Type "B" - Gata "Otsu"), the Western name of the tank is Type 89B I-Go Otsu.
The Type 89B is one of the world's first mass-produced tanks with a diesel engine, and the only mass-produced Japanese tank with rear-wheel drive. On Japanese websites and in literature, the name Type 89 and the name "I-Go" are written separately, and this applies to other Japanese tanks. Only in Western sources and in our country are they written together. Just like story with the names of American tanks. For example, in America it is called the Medium Tank M4, in England it was called "Sherman", and the rest of the world knows it as the Medium Tank M4 "Sherman".
In 1937, the army switched to a new system for naming armored vehicles, the Iroha system, where each prototype received a code name consisting of the tank type and the development number. Under this system, the name "I-Go" was changed to "Ti-I", which means "Medium First" (チイ). The Japanese Wikipedia says that the Type 89A became the "Ti-I", the Type 89B became the "Ti-Ro", but there is no other information about this anywhere (maybe more will appear).
In the appendix to the post-war memoirs of the Fourth Army Research Institute, both the Type 89A and Type 89B are designated as "Ti-I", which raises the question of the name "Ti-Ro". But this name was not popular in the army, since it came too late, and the production of the tank was ending. The name of the tank "Chi-Ro" ("Ti-Ro", not "Chi-Ro" - the second medium) appeared in Western sources only after WWII, and it applied to all Type 89 tanks. And also because the first experimental heavy tank was allegedly called "Ci-I" ("Ti-I"), therefore the Type 89 became "Chi-Ro".
It seems that in the British Army in September 1941, tanks that were in production were renamed, for example: Tank Infantry Mark II became Tank Infantry Matilda; and Tank Infantry Mark I did not receive a new name because its production was finished. The transcription of the tank's name is given according to the Polivanov System - it is also called "rosiyadzi" or "kiridzi".
Starting with the Hagel reference book, fictitious names for tank modifications appeared (Type 2592, Type 2594). Why D. Crowe and R. X called it "Chi-Ri" ("Chi-Ri" - middle ninth) is completely unclear. In English translation, the name would be "I-Go" ("I-Go"), not "Yi-Go".
Versions about the tank
There are several Western versions of what the modifications of the Type 89 tank are called, here are just some of them:
Version 1: The 1929 model tank was called Type 89A, 2589, gasoline engine; the 1932 modification was called Type 89B, 2592, gasoline and diesel engines; the 1934 modification was called Type 94, 2594, diesel engine 8150, 160 hp. Where mentioned: Fedoseyev, Sergeev, Baryatinsky, Heigel, Tomczyk, Rickard J.
Version 2: The 1929 model tank was called the Type 89A, gasoline engine; the 1932 model was called the Type 89B, gasoline engine; the 1934 model was called the Type 94, diesel engine. Where mentioned: aviArmor, Crow & Icks, Japanese tank and antitank warfare, Chant, Foss.
Version 3: The 1929 model tank was called Type 89A — gasoline engine; the 1932 modification and the 1934 modification were called Type 89B — diesel engine. Where mentioned: An.Wiki, tanks-encyclopedia, Chamberlain, Ellis.
In Japan, there are several versions of the names of the modifications of the I-Go tank, here are the last two:
The old Japanese version refers to the Type 89A tank — a model with a gasoline engine and two body options, with a broken front plate and with a solid sloping front plate (1932 version). But the course machine gun is located on the right, and the driver is on the left. The suspension is of an early model. And the Type 89B tank includes vehicles with a solid sloping front plate (1934 version), the machine gun is moved to the left side, and the driver's seat is now on the right. But the main thing is that a diesel engine is installed, as well as a late type of suspension. Where mentioned: Hara, Zaloga.
As a result of research in the new Japanese version of the I-Go tank, tanks with a Type 89B hull, but with a gasoline engine installed and small external differences that are not very visible, are also classified as Type 89A modification. At the same time, the Type 89B modification with a diesel engine was preserved, this is written below.
For my convenience, I use alternative names for the Type 89A tank modifications: early type (1929) - Type 89A-1, transitional type (1932) - Type 89A-2 and late type (1934) - Type 89A-3 (the same names are sometimes found for the T-54 - T-54-1, T-54-2, T-54-3).
And now how different modifications were and are called in books and on websites:
Early type: Japanese. Wiki (Type 89A); Tokizawa (Type 89A); Fedoseev (Type 89); Baryatinsky (Type 89A “Chi-ro”); Sergeev (Type 89A "Chi-Ro"): Ro. Vicky (Type 89 A); An. Wiki (Type 89A); Hara (Type 89A); Tomczyk (89A Chi-Ro); Ledwoch, Solarz (Type 89A); Chamberlain, Ellis (Type 89A); Crow & Icks (Chi-i, 89A); Tank Encyclopedia (Type 89A I-Go); aviArmor (Type 89 Ko); sensha-manual (Type 89 "Ko").
Transitional type: Japanese Wiki (Type 89A); Tokizawa (Type 89A); Fedoseev (Type 89); Baryatinsky (Type 89B “Otsu”); Sergeev (Type 89B, 2592, “Otsu”): Ro. Vicki (Type 89 V?); An. Wiki (Type 89A); Hara (Type 89A); Tomczyk (89); Ledwoch, Solarz (Type 89); Chamberlain, Ellis (Type 89B); Crow & Icks (Chi-i, 89B, 92); Tank Encyclopedia (Ttype 89B I-Go); aviArmor (Type 89 Otsu); sensha-manual (Type 89 "Ko").
Late type: Japanese. Wiki (Type 89A); Tokizawa (Type 89A); sensha-manual (Type 89 "Ko").
Otsu type: Japanese. Vicki (Type 89B); Tokizawa (Type 89B); Fedoseev (Type 94); Baryatinsky (Type 94); Sergeev (Type 2594 "Chi-Ro"): Ro. Vicki (Type 89 V); An. Vicki (Type 89B); Hara (Type 89B); Tomczyk (Type 2594 Chi-Ro); Ledwoch, Solarz (Type 89B); Chamberlain, Ellis (Type 89B); Crow & Icks (Chi-ri, 94); Tank Encyclopedia (Ttype 94B I-Go); aviArmor(Type 94); sensha-manual (Type 89 "Otsu").
Creation and production
On March 28, 1928, a decision was made to develop a light tank weighing 10 tons and with a maximum speed of 25 km/h, with the ability to overcome a trench more than 2 m wide, with a 57 mm gun and 1 machine gun, armor capable of withstanding fire from 37 mm guns from a distance of 500-600 m, dimensions that allow it to be transported by rail. Its main task was to support the infantry. The basis for its design was the British Vickers Medium Mk. C tank, purchased by the IJA in 1927.
The Fourth Research Institute of the Army Technical Headquarters began developing a light tank and completed the initial design in August of that year. In 1929, the design was sent to the Osaka Arsenal, where the "Experimental Tank I" had previously been built. The prototype was completed in April 1929, using armor plates taken from the Vickers Medium Mk C (version), while other experimental tanks of the time used mild steel. The armor steel created for armored vehicles was called "Niseko", and was developed by Nippon Steel Works in 1924. At that time, the industry was not yet able to produce armor steel, and the steel production process was developed and mastered later.
From April 1929 until December, the prototype was tested. In October 1929, the tank successfully passed the 660 km range test between Tokyo and Aomori. In the same month, it was temporarily standardized. Initially, the prototype was classified as a light tank due to the planned weight of 9,8 tons, but the combat weight increased to 11,8 tons. Based on the test results, due to the need to have domestically produced tanks, it was nevertheless standardized as the Type 89 light tank and received the name "I-Go", and in 1931 its mass production began.
The Type 89 was the first mass-produced Japanese tank. The first modernization of the tank was carried out in 1932, and the next, major one, in 1934. In 1935, the tank was reclassified as the Type 89 medium tank, and two versions of the tank with different types of engines began to be produced: the carburetor Type 89A (Type "Ko") and the diesel Type 89B (Type "Otsu").
Mass production was carried out by the privately owned Mitsubishi Aircraft Corporation (now Mitsubishi Heavy Industries). On December 1, 1929, Mitsubishi Aircraft opened the new Oi Plant as a tank plant, and the Nagoya Plant and the Shibaura branch were converted into the Tokyo Plant. In late 1931, the Japan Steel Works, Kobe Steel, and the Japan Railway Manufacturing Company also joined the production.
In 1937, the Tokyo Maruko Machinery Works of Mitsubishi Heavy Industries was founded in Shimomaruko, and from 1938 it began operating as a tank factory assigned by the army. The factory produced 6% of domestic tanks. Production of the Type 89 tank continued from 1931 to 1939, by the end of 1934, 220 Type 89A tanks were produced, and from 1935 to 1939, 184 Type 89A and Type 89B tanks were produced. By tank versions: Type 89A - 278 (283, possibly 5 pre-production) units were produced and Type 89B - a total of 126 units were produced.
Vickers Medium Mk.C prototype
The development of the new light tank Vickers Mk.C began in 1925. It was based on the chassis of the Birch Gun self-propelled gun, which was developed in 1923-24. From light, it was quickly transferred to medium tanks. This machine became known as the Vickers Medium Mk.C. When developing the tank, developments were used for the Vickers Mk.A and Vickers Mk.B projects, which used the "fire hedgehog" concept, that is, many machine guns along the perimeter.
The control compartment was located in the front, with the driver-mechanic sitting in the center and a machine gunner to the left of him. In the sloping frontal plate of the hull, to the right of the driver-mechanic, there was a door for the crew to enter and exit. The tank crew consisted of four or five people. A special protrusion was made in the frontal plate of the hull for the driver-mechanic's feet. The control levers were located on either side of the driver's seat. The gas and clutch pedals, as well as the gear shift lever, were located in the protruding part of the front panel. The crew consisted of a commander, gunner, driver, and loader. Various sources mention a fifth crew member (machine gunner?).
6-cylinder engine aviation The 110 hp Sunbeam Amazon II, which had water cooling, was located in the rear of the hull. The sides of the hull were flat, with protruding sponsons for machine guns and fuel tanks located above the tracks. The width of the tank was 2,5 m, the length was 5,33 m, and the height was 2,4 m. The tank could overcome water obstacles 1 m deep and trenches 2 m wide. The mass of the tank was about 11,6 tons. The thickness of the Mark C armour reached only 6,5 mm. The armour plates of the bottom of the tank were only 5 mm.

The Vickers Mark C's suspension was based on the Birch Gun and had a drive sprocket at the rear and an idler at the front. The Mark C had six pairs of bogies, plus an extra wheel behind the front idler. Like other British medium tanks, the wheels were suspended by vertical coil springs and the suspension was covered with mudguards. The Mark C used tracks that were different from those used on other tanks. The track links were rectangular in shape with cubic recesses in the middle. The width of the tracks was 305 mm, and the average pressure on soft ground was 0,49 kg/cm².
Vickers decided that a low-velocity 6-pounder (57 mm) gun would be sufficient to combat both infantry and vehicles. The origins of this gun are unknown, and it was apparently never mounted on any other tanks than the Mark C and Mark D. The Mark A and Mark B designs had a rear control post with a machine gun, which was abandoned. To control the rear hemisphere, the machine gun was placed in a developed rear niche of the turret. The machine gun could turn 60° horizontally and 20° upwards, 10° downwards vertically.
The machine gun located in the front part of the turret was removed. There were three machine guns in the hull of the tank, one of the machine guns was located in the front, to the left of the driver. Like the machine gun in the turret, it could fire at an angle of 3° horizontally and 60° vertically. Two more machine guns were symmetrically located in sponsons on the sides of the hull. They could cover an area of 30° horizontally and fire only at targets located directly in front of the sides. The tank was armed with four 60 mm Vickers water-cooled machine guns and had 7,7 rounds for them.
The Vickers Medium Mk.C entered testing in 1926, the only advantage of the tank was its speed, everything else turned out to be worse than that of the Medium Tank Mk.II. The tank was delivered to Japan in March 1927, where it was initially listed as a light tank, but was quickly renamed a medium tank. The official arrival of the tank took place at the Toyamagahara Army Parade Ground in Tokyo. Upon arrival, the tank was given the number 204 and was sent for preliminary testing. During one of the test runs, the tank caught fire, and two Vickers engineers conducting the tests received serious burns. The damaged tank, without a working engine, was sent to the Mitsubishi Nagoya Machinery Works Shibaura plant for repairs. A few months later, a new engine was delivered from England, and the tank was repaired. The tank itself was intended only to be used as a standard in the development of domestic tanks. After the Japanese military developed their own tanks, the Mark C was no longer needed and was most likely scrapped. Another version is that the armor plates were removed and used on the Type 89 prototype.
Устройство
The Type 89 tank had a classic layout. The control compartment was located in the front part, behind it was the fighting compartment, in which the tank commander was located on the right, and the loader on the left, at the end of the hull was the engine and transmission compartment. The turret and hull of the I-Go were entirely assembled on the frame using rivets. The armor thickness was determined as a result of firing tests at a distance of 150 m with a Type 11 infantry gun (caliber 37 mm) and was 17 mm. However, a 7,7 mm armor-piercing bullet easily penetrated the frontal armor. The side fender niches in the middle of the hull hang over the tracks, they are where the fuel tanks are located. On the upper surface of the fender niches are located: on the right side of the body 3-5 caps of the filler necks, and on the left 3-4 caps.
The Type 89 tank had a classic layout. A water tank was installed in the rear part of the left fender niche, which provided a supply of cooling water for the water-cooled gasoline engine and drinking water for the crew. There was a tap on the left rear wall of the fighting compartment. This was common to all Type 89s, but in the Otsu it was intended exclusively for drinking purposes. The fighting compartment and the engine-transmission compartment were separated by a bulkhead made of asbestos-cement plates, on the right side of the bulkhead there was a door connecting the fighting compartment and the engine compartment. For boarding and disembarking the crew, there was a hatch in the front plate with a hinged door, as well as hatches on the tank turret.
A stroboscope in the form of a rotating disk with radial rows of holes was mounted in the driver's inspection hatch cover. Later, the disk with radial slots was replaced by a disk with small holes. While providing a sufficient field of view, it was only suitable in good lighting conditions. Since about 1933, the driver's stroboscope received an armored cover with an arched cutout. During movement, removable armored glass was installed inside the inspection hatch. A mudguard was riveted under the driver's inspection hatch.
On the sides of the control compartment, two headlights were mounted on adjustable brackets from the inside. On the transitional version of the Type "Ko", instead of two headlights, one was installed, retractable in the front central part of the body (with a two-stage "bright/dark" switch). It was equipped with an armored cover for protection. There were no means of communication on the tank. Towing shackles were hinged to the hull at the front and rear. To overcome wide ditches and trenches, a folding "tail" was installed on the tank, which was attached to the rear armor plate and on which it was possible to transport a box of spare parts and a camouflage net. In addition, an additional battery was installed in the "tail", and barrels of fuel were transported on it.
The tank was equipped with three different turrets, not counting the prototype. The prototype turret was slightly conical in shape with a 6,5 mm Type 3 machine gun mounted in the rear of the semi-circular turret. The front of the turret, where the gun is located, is flat. From above, it looks like a drop.

I sorted the turrets in the order they were installed on the tanks. I called them Type 1, Type 2, Type 3, and did not take into account the prototype turret (to differentiate).
The Type 1 turret is similar to the prototype turret, rotated 180º, the front part is semi-circular, tapering to the rear, where a machine gun is mounted in the flat part. On the right, at the rear of the turret, next to the machine gun, there is a small hatch. On the left side of the turret there is a rotating observation window, on the right side of the turret it was removed. The turret is symmetrical in shape with a slight angle of inclination of the sides. Instead of one hatch on the roof of the turret there are two hatches, left and right. The right hatch is located under the cupola.
The Type 2 turret is similar to the previous one, but slightly turned to the right, the front part is semicircular, it has a slightly conical shape, in the back in the flat part there was a machine gun, turned to the left. On the Type 3 turret, the front part is made flat, and in the back there is a machine gun (as well as on the Type 2). The turret itself is asymmetrical, complex in shape, with an extension protruding from the driver's side, in which a machine gun is installed. The hatch became the only one, double-leaf, and is located on the roof of the observation turret. On the left side of the turret, the rotating observation window was removed. On the right side of the turret, a mount for installing an anti-aircraft machine gun is installed.
The Type 1 and Type 2 turrets were equipped with a narrow vertical, slightly conical observation cupola with 4 observation slits during production. There was a hatch under the cupola. During production, the Type 2 and Type 3 turrets were equipped with a large observation cupola ("mushroom") with a two-piece hatch on top. Over time, all tanks with Type 1 and Type 2 turrets produced in 1933–1934 received a new commander's cupola ("mushroom") during modernization.
The first series of tanks was equipped with a 37 mm Sogekiho (狙撃砲) cannon, exactly the same as the Renault Type A and Renault Type B tanks. Only the first five vehicles were produced with it. The tank did not have a gun mantlet, which caused a noticeable gap to form when the cannon was raised, through which bullets entered the tank. This was only discovered during the first combat operations, after which the problem was solved.
After the start of production of the new 57 mm Type 90 cannon, it was installed on the tank. The gun elevation angle was from -15 to +20 degrees, which allowed the gun to be turned 10 degrees to the left and right with the shoulder rest even with a stationary turret. The barrel length was 18,5 calibers, the projectile weight was 2,57 kg, the muzzle velocity was 350-380 m/s, the sighting range was up to 800 m. Armor penetration at a distance of 500 mm or less was 20 mm. In 1937, the cannon was replaced with a new Type 97 cannon. Its ammunition load included armor-piercing shells.
The rear of the turret and the frontal hull plate on the right housed 6,5 mm Type 91 machine guns, each mounted in a ball mount along with a bipod and telescopic sight. The prototype and Early Type tanks had Type 3 machine guns. The apple support could be adjusted to three fixed positions to adjust the depression and elevation angles. There was a hatch at the rear of the turret on the right side. The machine gun, mounted in the turret and directed backwards, was intended to fire forward, in the direction of the tank (when the turret was turning), which allowed firing from 2 machine guns. In particular, shooting from the turret is quite convenient, since it has a higher firing altitude than that of infantry.
In the rear part of the hull, on the right side of the Type 89 tank, there was a 4-stroke 6-cylinder in-line Daimler carburetor liquid-cooled engine with a capacity of 115 hp/1800 rpm, later replaced by a 4-stroke in-line 6-cylinder Mitsubishi carburetor liquid-cooled engine with a capacity of 118 hp/1800 rpm. On the right side of the engine compartment there were two rows of Sirocco fans that cooled the engine and ventilated the fighting compartment. The Type 89B tank was equipped with a 6-cylinder in-line Mitsubishi A6120VD air-cooled diesel engine. The gearbox was four-speed with one reverse gear, main and side clutches, and mechanical brakes. On the Type 89B tank, the gearbox was improved. Access to the transmission units was provided through hinged rear hatches. It is mentioned that the Type 89B was equipped with a 160 hp diesel engine, but this is not true, because it simply did not exist. This is another of the invented versions.

The tank used a modified and simplified version of the Vickers Medium Tank Mk. C suspension. The chassis on the prototype and production vehicles was similar, but on the production vehicles it was modernized. On production tanks it was of two types, let's call them "Early" and "Late".
The chassis consists of nine double solid support rollers of small diameter, eight were locked in pairs into bogies, two of them were hinged at the ends of the balance beam and together with it were suspended on a semi-elliptical spring on the side of the hull. The front roller had an independent spring suspension. On the chassis of the type "Early" and the prototype there were five support rollers, which were mounted on a single beam. In the suspension system of the type "Late" the guide wheel protrudes 50 cm forward to increase cross-country ability in trenches. In addition, the suspension is lowered by 15 cm, and the gap between the lower part and the surface of the body increases. There are now 4 support rollers. In addition, the support frame of the support rollers is removed.
The chassis was covered with 6 mm armor screens, which differed in appearance on the "early" and "late" suspension. The track was a large-link steel pin engagement with one ridge. Over time, the track was replaced with a small-link one with lugs. The track width was 305 with a track pitch of 150 mm. Specific pressure, kg / cm2, - 0,65. The driving wheel with a diameter of 762 mm with pin engagement was located at the rear. The toothed rims of the guide wheel are similar to the driving one, it was located in front and had a diameter of 914 mm. On the Type 89 prototype, the wheels were spoked, and on serial tanks they were replaced with solid ones. The track tension adjustment mechanism is screw-type, located at the front.



Type 89 Medium Tank Versions
In the Imperial Japanese Army, the Type 89 tank was classified as follows:
Tank Type 89A (Type "Ko")
— prototype;
— early version;
— transitional (medium) version;
— late version;
Tank Type 89B (Otsu type).
Differences between the Type 89A and Type 89B tank models
The difference between the Type Ko and Type Otsu models is the engine type. The Japanese Army calls the I-Go tank with a gasoline engine the Type 89A, and the I-Go tank with a diesel engine the Type 89B. However, the engine type cannot be determined from the outside. They differ in the following indirect features:
1) fuel tank caps on the fender niches;
2) the engine carburetor air intake cover;
3) grilles on the engine compartment;
4) hind wings.

The diagram shows Type "Ko", late version (taken from Takizawa's website).

Differences in the engine section of the hull, rear fenders, and fender niches in the modifications: number 1 - Early Type 89A without a carburetor air intake cover, number 2 - Transitional Type 89A already with a cover, number 3 - Late Type 89A and number 4 - Type 89B.
A surviving Type Otsu tank is on display in Japan at the School Museum artillery weapons of the JGSDF (Japanese Self-Defense Forces), which is located in Tsuchiura, Kanto. And that one is spoiled by the restoration that was carried out - asbestos sheets were stripped off, a modern engine was installed, etc.

The diagram shows:
1. Early Type 89A with 37mm gun and Type 1 turret, 5 produced,
2. Type 89A early type 57mm gun, Type 1 turret,
3. Early Type 89A with Type 2 turret,
4. Type 89A transition type with Type 2 tower,
5. Type 89A transition type with Type 3 tower,
6. Type 89A late type with Type 3 turret,
7. Type 89B with Type 3 turret.
Tank prototype
In October 1929, the prototype passed tests and was officially recommended for serial production. It was created on the basis of the Vickers Medium Mk. C. The tank used a modified and simplified version of the Vickers Medium Mk. C suspension. The tracks were steel, large-link, skeletal. Headlights were installed on the left and right sides of the front of the vehicle.

The prototype's frontal armor was installed vertically. On the lower panel, to the right of the tank's center, where the machine gunner sat, there was a hatch for the crew to enter and exit. The driver's seat had a protrusion, like on the Vickers Medium Mk. C tank. In the driver's compartment, the driver was located to the left of the tank's center and had an observation hatch. A strobe light was installed in the driver's observation hatch, which was a rotating disk with radial rows of holes. The machine gunner was located to the right and controlled the Type 3 machine gun, fixed in the frontal armor. To the right of the machine gunner was the ammunition supply, a total of 2800 rounds for the machine gun. To the right and left of the tank's center was the ammunition for the gun, 110 shells. The turret was slightly conical in shape, with a second 6,5 mm Type 3 machine gun mounted in the rear of the semi-circular turret. The front of the turret, in which the gun is located, is flat. There are rotating observation ports on both sides of the turret. There is one embarkation hatch in the turret. The tank commander also served as the gunner, and the loader also used the machine gun in the rear of the turret. The tank's weapon was a 57 mm Vickers gun, since the 57 mm Type 90 gun was still under development.

The prototype used a licensed 6-cylinder Daimler water-cooled gasoline aviation engine with a capacity of 100 hp, which was located on the right in the rear part of the hull. Between the fighting compartment and the MTO there is a bulkhead in which there is a hatch for access to the engine, and access is also provided through hatches in the roof of the engine compartment. The hull was lined with asbestos sheets from the inside. Power was supplied by a 180 Ah battery. The fuel tanks were located on the sides of the hull, in the fender niches. On the upper surface of the fender niches there are; 5 filler caps on the right side of the body, and 4 caps on the left. In the MTO, to the left of the engine, there was an engine radiator and an oil tank.
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