“O-I Kai” – potential tier 8 Japanese HT premium

Wargaming has recently been intensively releasing more and more premium vehicles. It is up to you to decide if implementing more is necessary. However, in my opinion if Wargaming really wants to implement more premiums, they should focus on implementing (tier 8) premiums for branches that doesn’t have one before adding more Soviet, US and French tier 8 premiums.

One of the branches with no tier 8 premium is the Japanese HT line (Nameless doesn’t count, heh). If one reworked the HT line like I have proposed in the past, it would be possible to make the O-Ni as a tier 8 premium. That is however only if you rework the line – otherwise it is not possible, unless you copy the O-Ni with buffs (or alternatively a slightly altered O-Ho) into a tier 8 premium. The O-Ni, however, is more or less completely fictional – it is born from some inaccurate artworks, combined together with false information and rumors regarding the actual O-I.

Despite that, I had the O-Ni as a tier 8 premium for the branch. However, after the rework proposal, I have come up with a better idea that can work as a tier 8 premium heavy tank vehicle for the Japanese branch. It is more unique – and somewhat historical… or well, let’s say that the background is at least historical. While the tank itself is more or less a “what-if” idea, the recent changes of Wargaming (such as all of those armor buffs, the Chinese TDs and the upcoming tier 9-10 French heavies, which are basically hull and turret combined together from two different projects, etc.) have opened a door for it.

Meet the “O-I Kai”.

Historical background

This vehicle is essentially a combination of a “what if” development that would have occurred between the O-I and Type 4/5 (O-Ro / O-Ro Kai) and a possible wooden mockup of the O-I that mounted a different, more powerful engine.

The same documents that contained the only known information regarding the Type 4/5 also contained information about a wooden mockup of the O-I that was under possession of the Red Army after WW2. The mockup replaced the ordinary twin gasoline engines with a liquid cooled V-12 diesel engine, which presumably was an uni. The model had two six-section radiators with an air flow achieved by exhaust fumes. The air is gathered by the engine compartment cover. An auxiliary fan helps to guide airflow over the engine and in return helps in cleaning out the fighting compartment, driven by the fuel pump motor. That’s about it however, no other information is known.

Kuvahaun tulos haulle type 2604

Engine schematics and a sketch drawing of the Type 5, or “Type 5 O-Ro Kai”, like it would likely have been designated as. The “O-I Kai” would be a logical development step towards this vehicle from the original, multi-turreted O-I.

“Logical” progression between the O-I and Type 4/5

We also need to look at the time period. Given the wooden mock-up is described with the Type 4/5 information, we can assume the vehicle is a later design than the regular O-I. Now we need to take a look at logical improvements.

The O-I project was terminated in 1943. The tank was one of the very last vehicles in history to carry multiple turrets. At this point, pretty much all nations accepted the fact that the multi-turret concept was a failure, and Japan was no exception – Type 4/5 also had just one turret. It would be logical to assume that one of the first improvements of the O-I would be removal of the mini-turrets. This saves the weight of the vehicle.

The O-I is designed with the mini-turrets in mind – which is why the upper part of the hull is so much higher than the lower part of the hull, and also why the tank was so wide (having two relatively large mini-turrets in one row requires increased width). The logical improvement is to lower the vehicle and make it narrower. Another thing is the thin tracks of the O-I, which are very narrow compared to the width of the vehicle. If we make tracks to around ~1000mm (1 meter) wide, the ground pressure wouldn’t be as big. Combine this with a significantly more powerful engine and lighter weight (~30-40 tons lighter than the O-I itself).

And now finally, the gun. A 150 mm howitzer could be still a logical choice given the role of the vehicle. However, with the removal of the 47 mm guns the tank loses anti-tank capacity (although at this point the 47 mm guns were not that powerful anti-tank weapons as they were in pre-WW2/early WW2). A logical, dedicated anti-tank weapon as main armament would be a 10cm Experimental Tank gun, which was developed for the Ho-Ri tank destroyer around 1943 and 1944.

Kuvahaun tulos haulle experimental 10 cm tank gun

10 cm Experimental Tank gun, designated for the Ho-Ri tank destroyer, as well as mounted in-game by the O-Ni and O-Ho. Later a designed, improved version was accepted into service under the designation “10 cm Tank Gun Type 5”, mounted on the production models of Type 5 Ho-Ri (aka the vehicle that was referred as “Ho-Ri III” in the past). The gun has a stray autoloader mounted on, which could be removed to fit the gun into the O-I’s turret.

The gun was developed and tested around the same time as the O-I Kai probably would have been developed. If one wants to improve anti-tank capabilities of the O-I Kai, the 10 cm Experimental gun would be the logical armament for the O-I Kai, as it was the most powerful dedicated anti-tank gun ever designed by the Imperial Japanese Army. You can think of it like this: the 10 cm replaced the 15 cm howitzer due to better anti-tank capabilities, however, having powerful HE shells was still considered to be necessary, which ended up being the case with the Type 4 and its 14 cm gun, which should be a better anti-tank weapon than the 15 cm howitzer, while it would have better HE shells than the 10 cm anti-tank gun. One thing to note is that the breech of the 10 cm gun is quite a bit bigger than the 15 cm’s (the 15 cm howitzer actually has almost no breech). One solution is to remove the stray autoloader (which is what I believe they actually did with the Chi-Se, which combines the 10cm gun with Chi-Ri II’s turret mounted on the Ho-Ri’s hull) to fit into the turret. If that doesn’t work, redesigning the turret might be necessary.

In World of Tanks

So, if we combine the engine of the wooden mockup and (somewhat) logical development steps that would have begun after attempts to fix the O-I and would have eventually evolved into the Type 4 O-Ro… the final design of the O-I Kai would possibly look something like this:

It does look quite funny indeed, but how would it actually perform in-game?

Let’s now assume that the armor of the O-I was considered sufficient enough. 150 mm is awesome for a tier 6 HT, but not so much for a tier 8 HT. In general, it would be quite unarmored for a tier 8 HT. However, increasing the armor is not necessary – you will see soon why. As for firepower, it would be decent but nothing absolutely spectacular. The 10 cm would be more or less like the 10 cm on the O-Ho, though it would function better here thanks to the more mobile platform.

So you have poor armor on an utterly massive tank with just a “decent gun”? Well, you can guess which is the strong point – yes, mobility.

If you shave off the mini-turrets, and make the hull narrower and lower, but give it a larger engine deck and engine, the mass would be roughly around 110-130 tons. The engine is not specified. However, looking at Japanese submarine engines, it is safe to assume that it would be… very powerful. Some potential submarine engines that would be fitted have 1850 HP, 2100 HP, or even 2250 HP (!). This is where things start to get very exciting.

Let’s assume the O-I Kai weighs 130 tons. Even with just the 1850 HP engine, the tank would have 14,3 hp/ton power to weight ratio. That is roughly 2 hp/ton more than the KV-5 and comparable to some slower same-tier mediums. However, with the 2250 HP engine… the power to weight ratio would go up to a whopping 17 hp/ton – yes, higher HP/ton than some top-tier mediums like Object 140With a twice as strong engine as the original O-I and still with a lighter mass, the top speed would be quite high – as the O-I was projected to have 30km/h top speed on a road, a lighter variant with a much stronger engine would very well potentially go 40-50 km/h on a road, though it likely would be still quite slow off-road due to the mass. Now imagine the ram damage done by a 130 ton tank with 150 mm frontal armor going over 50 km/h downhill…

O-I Kai

Conceptual schematics that represent how the “O-I Kai” would have looked like. It is an evolution of the O-I with logical improvements: such as a narrower, lower hull, no mini-turrets, a different main gun, higher engine deck to house a bigger and more powerful engine and significantly wider tracks. A lot of similarities with the Type 4/5 can be seen as well.

  • Hitpoints: 1700 HP
  • Armor (hull): 150 / 70 / 150 mm
  • Armor (turret): 150 / 150 / 150 mm
  • Mass: 130 tons
  • Top speed: 50 / 15 km/h
  • Engine power: 1850 – 2250 HP (depending on which engine WG would pick)
  • Power-to-weight ratio: 14.3 – 17 hp/ton
  • Gun: 10 cm Experimental Tank gun Kai
  • Damage: 330 / 330 / 430
  • Penetration: 215 / 254 / 53 mm
  • Depression/Elevation: -10° / +20°
  • View range: 380 m
  • Signal range: 750 m

Basically, the vehicle would play very much like the pre-9.20 O-I Experimental, just without the thing that made the vehicle truly overpowered – the gun with overly excessive alpha damage. The O-I Kai wouldn’t have even close as good firepower as the O-I Experimental had with the 10 cm gun and it would be huge and the armor would be quite useless against same and higher tier tanks.

There are few other options on how the O-I Kai would be implemented in-game. Optionally, increasing the armor a bit at the cost of its mobility (which would make the vehicle essentially a Japanese KV-5, with some major differences like way better penetration but no preferential matchmaking) is one possibility, if the vehicle feels too extreme. There are quite a few other guns that could be used, including a 10 cm with it’s stray autoloader mounted on, 12 cm, 12.7 cm or 15 cm, but I opted for the single-shot 10 cm instead.  As for the 15 cm gun, I would personally avoid using that, despite those guns being a “speciality” of the (as they are right now) Japanese heavies. However, I personally feel like that a premium vehicle that goes 40-50 km/h with the ability to do 900 damage with a penetrating HE shell among with the ramming capabilities is not… a very good idea. The 12 cm and 12.7 cm guns would be balance-able (if you make the vehicle a bit slower, especially with the 12.7 cm’s case, which would require a much bigger turret), but I opted for the single-shot 10 cm to be able to keep the high mobility of the vehicle.

Potential gun and turret options of the O-I Kai. From top to bottom: 10 cm without autoloader mechanism, 12 cm, 15 cm, 10 cm with autoloader mechanism and a bigger turret, and finally a 12.7 cm with a turret from the Type 4. The last variant is imagined with a bit different idea of combining the Type 4 turret and a modified hull of the O-I together and would be quite a bit different in terms of playstyle (way more sluggish but very good turret armor). 


I expect that this vehicle would be quite popular, just because how hilarious ramming capabilities it has – and people love seeing three (or in the O-I Kai’s case, even four) digit ram damage numbers, don’t they 🙂