Reviewing this as someone who has extensively played the Japanese heavy line since their release in 2015, and 3 marked every single Japanese heavy tank.
Review is based on patch 1.17.1.
- Great HP pool (1060)
- Arguably the most heavily armored tier 6 - very hard to penetrate frontally with less than 160 mm penetration
- 15 cm derp gun has extreme power behind it - the 700 alpha AP shells are lethal, and the HE can oneshot many lower and same tier vehicles
- 10 cm has great alpha damage (100) and one of the best penetration values of tier 6 heavies (175 / 201)
- Great gun depression (10 degrees)
- Great view range for its tier
- Absurdly heavy for its tier (150 tons). Not only its practically completely impervious to ramming against literally any tank it can face other than the VK 168.01 (which the O-I will very rarely fight, anyway), the O-I can also cause humongous ramming damage by itself.
- Decently thick rear armor that can resist some lower tier vehicles
- Huge and fat. By far the biggest tier 6 - you're literally at least twice as big as pretty much any other tier 6
- Slow mobility, struggles to reach its top speed
- Flat armor that kinda stops working against +170 mm pen. Premium ammo and higher tiers will butter through you pretty easily
- Very weak side armor
- 15 cm has awful dispersion, low penetration, very long reload and the HE shells can be a bit unreliable
- 10 cm has atrocious DPM and gun handling
- 10 degree gun depression is mostly fake - its 10 degrees only directly at the front, between the miniturrets
Equipment: Personally, I run Improved Ventilation / Gun Rammer / Improved Aiming Unit, but other than the Rammer, which in my opinion is mandatory, the two other slots are completely optional.
Seriously, the O-I actually has a huge amount of options and I feel like there isn't a truly obvious choice. In my opinion, Improved Hardening isn't as good here due to lower HP pools at tier 6. Turbocharger also doesn't help the O-I quite as much as the other Japanese heavies, as it has higher top speed that it already struggles to reach. Turbo is still a great choice, though, as extra engine power never hurts. Other very viable choices include Improved Aiming Unit, which is very useful to boost derp gun's accuracy, Vents, which further improves poor reload, dispersion and also boosts view range, Improved Rotation Mechanism, which is another way to boost gun handling, and even Coated Optics for a very spicy view range.
I run Vents / Rammer / IAU to maximize accuracy, which allows me to land meaty AP/HEAT shells as accurately as possible. However, again, the equipment choice on the O-I really does feel like its up to a personal preference.
The review itself:
If you're looking for one, just one, somewhat decent tank in the Japanese heavy line, then look no further. The O-I is there to save your day. You gotta give a credit to a tank that has been nerfed directly THREE times and then indirectly a fourth time with HE rework, while somehow still managing to be a decent vehicle. Sure, compared to the hilariously overpowered 2015 O-I, the O-I can seem like a shadow of former itself. But that's a good thing - the O-I used to be hilariously overpowered, so it kinda had to be toned down significantly. Obviously, the HE rework did shake things up quite a bit. The O-I was definitely hurt by it, and thus isn't quite as braindead to play as it used to be. But unlike what some people believe, the O-I is far from being a worthless vehicle. It still has one of the higher winrates at tier 6, though I believe the non-existent stock grind is a important factor here. Really, I don't really even perform worse at all after the HE rework than I did prior the HE rework. The O-I can still be a beast, it's just not very consistent and can be really unwieldy.
Lets talk about the guns first. The O-I comes with two gun choices: the 10 cm and the mighty 15 cm derp gun. The former is a pretty alright gun, but suffers from laughably awful DPM and gun stats. Its not the worst gun around, but the O-I is kinda a worse T-150 with it, so unless you really hate derp guns and don't aim to keep the O-I, I recommend using the derp gun, as that's what makes the O-I...the O-I. The HE rework did greatly affect how to use the derp gun, obviously. You can no longer point + click at somebody and expect to do 300-400 damage every time. The HE is still very useful, but it's much more unreliable. The main trick is not to spam HE - your main ammunition is actually AP and HEAT. You see, 121 mm AP pen with excellent overmatching capacities...actually isn't awful at tier 6. 150 mm HEAT is also very useful for higher raw pen. Yeah, the AP and HEAT can be unreliable, but just a few pens can already net a monster result. To make this work, you NEED the Intuition crew skill. It lets you have AP/HEAT loaded most of the time, and then when you face something that is either HE pennable or you know you can't pen with AP/HEAT, then you reload the HE shell, wait a few seconds, and use it to deal at least some damage rather than none. Yeah, the HE isn't as good as it used to be, but it actually can still deal pretty decent damage as a lot of tanks the O-I faces don't really have that thick armor.
Once you get to learn to play around with different ammo types, the O-I itself is still very simple. Its slow and the armor is just...there. You kinda just, stick your front and bounce tanks you can bounce, and don't bounce when you don't. Don't get overconfident with the O-I's armor - its strong for its tier, but you shouldn't rely on it, unless you face tanks you know they can't pen you. You generally want to find targets that you can penetrate with AP/HEAT. Remember, just 2-3 pens is enough to have a good game. Learn what tanks you can penetrate and what not, what areas are overmatchable with AP, what tanks can be penetrated with HE, and so on. Again, remember to get the Intuition skill. Also, O-I's absurd weight can result in some hilarious shenanigans if you get to ram somebody. Even with the O-I's slow speed, its so stupidly heavy that simply tapping someone will result in massive damage.
Overall, the O-I is still a capable and fun machine. It requires a few more braincells to get it to work than it used to require, and you know what? I think that's fine. It requires a clever use of all 3 ammo types and demands good positioning more. Because of this, personally to me, the O-I feels more rewarding to play when you master the few little tricks. It's not a consistent performer, as it really tends to either do nothing, or get monster games. But you should expect that from a 150 ton mega massive box wielding a 15 cm derp gun.
If you're looking for a keeper on the Japanese heavy tank line, this is the one. Unfortunately, you could say that the O-I is both the start and the end of the Japanese heavy line. The rest of the Japanese heavy line sadly gets way worse after the O-I.