Thursday, October 20, 2016

Between a Bolt and a Hard Place

   In modern interpretations, Japan is often seen as designing tanks held together by numerous bolts and rivets. A concept considered elegant in the inter-war period, but outdated during the war as new and more reliable methods of cast and welds become mass preferred upon in competing nations. The most iconic tanks grouped with Japan are vehicles designed and manufactured as early as 1934, nearly 7 years prior to the introduction of the infamous American M4 Sherman and Russian T-34. By the time the Second World War initiated, Japan had since started to deviate from their reliance on bolted tanks.

However, when you see the O-I up and about, the first thing you may notice are the bolts blanketing the tank's entirety. Don't be confused, the bolts on this superheavy vehicle are only a camouflage for the secrets lying underneath the steel. In first glance, the tank's design comes off as simple, flawed, and simply over excessive. It's design, albeit massive and complex, was given a simple and straightforward goal. That being as an armoured bunker in Manchuria, not as a combat tank to engage alone in the field.

FineMold's O-I 150t model - The company that purchased the newly shown O-I reports.

The O-I was conceived out of the necessity to produce a mobile bunker to contest the Soviet Union in the then-expected Second Russo-Japanese conflict. The flaw with the routine bunker or pillbox is that you cannot maneuver and relocate them with the frontline constantly being pushed. Japan would need a sustainable fortress that could push with the infantry and advance further into the USSR without the need to construct more immobile bunkers with resources already scarce.

Japan relied on the North Expeditionary Doctrine when dealing with the threat of the USSR. After the defeat at Khalkhin Gol, the Government practically outcasted the Imperial Japanese Army for embarrassing Japan while its Navy met unrivaled. However, to counter their prior loss they had planned to once again prepare for another conflict that had seemed inevitable with the initiation of the German invasion of Poland and declining of relations. The tank was designed to withstand the guns of the Soviet Union's arsenal, while all the same countering with use of a 15cm howtizer against enemy positions and advancing armour.

Type96 15cm Howtizer - Main armament of O-I

O-I's main armament was chosen to be the newly produced Type96 Howitzer. A 4,140 kilogram cannon built and pressed into service in 1937, the cannon saw extensive use against the National Revolutionary Army in China and during the border conflicts with the Soviet Union. The cannon was picked to accommodate the need of targeting enemy fortified positions to cover the Infantry's pushes. By design, this is not an anti tank armament, it does not have wide options of anti tank shells with high penetration. The main shell of the howitzer is the Type95 APHE shell, recorded with 540 m/s and an average penetration of 125mm at a range of 230 meters. The cannon saw useage of both the Type92 HE and High penetrating HE shells respectively.

Type1 47mm anti tank gun
The tank was not only given the 15cm howitzer, however. Located on the front hull, two turrets with a Experimental 47mm's were present. Today we know the cannon as the main gun of the Chi-Ha Kai. This cannon was introduced in 1940 and became the nation's primary gun for anti tank measures. With penetration ranging from 80 to 114.3mm depending on the individual shell type.  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 O-I was designed with 150mm of total armour thickness in both the front and rear of the vehicle. However, the production of the tank proved difficult to manufacture a 150mm plate, so to counter this crossroad, Mitsubishi split the plate into two separate slabs of 75mm armour thickness. The second 75mm plate would be bolted and sealed onto the existed plate on the vehicle to provide the expected over all thickness of the tank. The side armor on the hull superstructure was 70 millimeters thick. the base having standard thickness of 35mm, supported by an additional 35mm plate bolted on. 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. On the lwoer half of the side, a measurement of 110mm of armour thickness is present. 40 ladder pieces were placed around the tank to provide crew with the ability to climb onto of the vehicle with ease.

Layout of the armour of the O-I, befitting of the name "mobile pillbox".

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. These proportions were massive and required the equally large amount of crew to operate it. The crew consisted of 11 manned positions. These were; 1 Driver, 1 Co Driver, 3 Main turret gunners, 1 Commander, 2 secondary turret operators, 1 rear turret operator, 1 Radio signaler, and 1 Engineer to maintain the tank. 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 output of the engine is 550hp, both combined gave the tank an over all of 1100hp. The tank had a 6 gear system and weighed 1020kg. Speed of the tank ranged in 40kmh on flat roads in the 96 ton prototype. Paper speed with 150t weight was 30. 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. Truly, a design of high proportions, with little feasibility for the weight of the expectations put on the tank.

This will be a 3 part series covering the O-I superheavy tank. Stay tuned for the final part where I cover what is fake and whats real about the O-I!


  1. Hello, this is AURICOM from War Thunder I would actually love to see this as a premium tank in war thunder simply because Gaijin would probably make this a rank 4 tank and everyone would gold rush it. But the main reason is that I would love to make use of the smaller turrets on the front of the tank. A 47mm gun will be useful for mainly tanks with less armor like the shermans for example. If the tank is added into the game it will be extremely useful on the city maps and will be a sitting duck on the open area maps. Good post and take care I look forward to reading more of your posts in the near future.

    1. Something to compete with the maus!!!

    2. If it is true that the O-I did exist at some point, I don't see any reason why they could not add it ingame. It's such a shame that it was scrapped...

    3. Please don't make it a premium, it is necessary to have it in the main heavy tank line of Japan due to the low amount of heavy tanks produced by the Japanese Army

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