A problem with Japanese armor research is that most of the records have either been destroyed by firebombing, burned up after the surrender to hide involvement, carried off to the United States where they became lost (along with perhaps problematic translations made), or kept sleeping in private collections. That is why there is relatively little material to work on, leading to endless copying of the same old research (and the accompanying spreading of myths, like a 88 mm gun for Chi-Ri). However, not all is lost, since even now there are new discoveries happening.
I’ve been looking through the archives recently at the National Institute for Defense Studies (when going to Tokyo on business), and came across two files which might be used to buff Chi-To, and by extension Chi-Ri, in the future. While I cannot guarantee anything, given that these are historical records, WG might include them for accuracy in later updates. We’ll see.
For your convenience, I’ve reverse-searched the digital versions of the files at the Japan Center for Asian Historical Record, so look there if you want to do research for yourself.
7.5 cm Tank Gun Type 5 Penetration
The current penetration for 7.5 cm Tank Gun Type 5 is based on two test records from late 1944:
1) Imperial Guards 3rd Division: 100 mm penetration at 1,000 meters
2) Research Team of Army College: 118 mm at 300 meters, 115 mm at 400 meters, 112 mm at 500 meters.
Using these as the basis, WG came to 124 mm for penetration at 100 meters. While it would be nice if I was able to see the documents myself, they are currently held by the JGSDF, making research very difficult. Thus, we relied on the writing of Japanese authors for these two.
Anyway, I came upon this document, which had the following chart:
Test plate: steel plate (not RHA) at 90 degrees.
Test Gun: 7.5 cm Tank Gun Type 5
Test Ammo: 7.5 cm Armor-Piercing Type 1
100 m: 200 mm
400 m: 180 mm
650 m: 160 mm
1,000 m: 140 mm
1,600 m: 100 mm
2,500 m: 60 mm
According to Japanese records, apparently steel plates had 20~25% less protection than RHA, although I frankly think it goes up even more for decent RHA. Supposing we use 30% less protection, it gives us something like the following:
100 m: 140 mm
400 m: 126 mm
650 m: 112 mm
1,000 m: 98 mm
1,600 m: 70 mm
2,500 m: 42 mm
Now, why did this happen? Frankly, I’m not sure, since the report is pretty straightforward, going immediately to “practical” applications of at what distance a Sherman, Churchill, and “M1″ Heavy (T1 for us) would be penetrate. In addition, the use of “steel plate” is troublesome, since it throws off our preception of what we’re dealing with. While it is true that steel plate was considered 20~25% weaker than RHA, this is quite off when the Soviets general used 50% off as their standard. All in all, what we can say is that the round had become more penetrating, as can bee seen at the 1,000 meter penetration (98 mm), which is similar to the Imperial Guards 3rd Division test.
If I am pressed to propose a theory, I would say that the downfall of the IJN was the leading factor in this. Despite IJA having received more funds, it was IJN that was technologically superior, with better propellent, better explosives, better access to good material (although not on an absolute scale amount). With IJN basically disappearing as a force from the face of the earth with continuous disasters, IJA could have a virtual monopoly. In addition to this, the loosening of IJA headquarters’ hold on research was lessened. Originally, IJA heaquarters had the tendency to interfere with the research of the engineers, which was why Japanese tank development was so retarded. Be it forcing the production of “hard” steel (leading to brittle plates that was easily destroyed by higher velocity rounds and problems with welding), delaying tank gun development on the grounds of unnecessity and rate of fire (apparently HQ demanded that guns be shoulder-supported, to ensure faster aiming and rate of fire, never mind limitations to caliber), or not keeping up with the times (asking for small upgrades when the engineers were already sure of greater ones). By 1945, much of the HQ interference was either lowered or ignored, with the example of Mitsubishi going its own way with armor plates to finally make RHA of world standard.
Of course, this is just speculation on my part, and frankly I’m not sure myself. What is known, is that by 1945 ammo quality had gone up, with even the US military noticing it. Thus, so far in WoT, we’re using 1944 results when by mid-1945 things have gone further.
Reference online: 『対戦車戦闘の参考（戦車関係）補遺』、アジア歴史資料センター。 C14060869100。
Chi-To Combat Weight
Sometimes you find unsuspected things while looking for something else. In this case, I came across the following while researching landing-crafts for my own personal reason of material for fiction writing:
This is the testing layout of the Experimental Large-Sized landing craft, basically a bigger and upgraded version of the Toku Daihatsu-class landing craft. It was 25 meters long, 4 meters wide, and 2 meters deep, with a fully loaded displacement pf 62.27 tons. It would have been able to go at a crusing speed of 8.9 knots for 2 days.
For our purposes, what is important in that drawing is the loaded tank. You can see that it is labeled “Chi-To”, along with the note “Fully Equipped Weight 29.5 Tons”. What is the importance of this? This is the first primary source I have seen of Chi-To’s combat weight. So far all we had were secondary information from researchers who were either involved in development (Hara) or related to them (Mitsubishi), and those measurements were of the prototype Chi-To at 30 tons. This primary source, which was written in 1945 when the production Chi-To was to come out, means that we have data that matches things closer to what the production Chi-To would have been like. Ultimately, this means we need to reduce the weight of Chi-To in the game.
As a side note, I have a theory on why this Experimental Large-Sized landing craft was supposed to be able to carry Chi-To. It was likely to be used to ferry Chi-To across straits to reinforce defending troops. Basically, since logistics was messed up anyway, IJA probably figured they might as well take chances individually instead of risking losing everything by sending in one boat. IJA had lost thousands of men and tons of supplies when a few transports were suck while being sent to reinforce New Guinea.
Reference online: 『設計／大型発動艇 一般配置図』、アジア歴史資料センター。 C12122163300
In conclusion, I have shown that the penetration of 7.5 cm Tank Gun Type 5 could be buffed, and combat weight of Chi-To could be reduced. While I doubt the former would be implemented for Chi-To (we already have a well-balanced gun), it can certainly be used to help buff Chi-Ri, with an estimated 175 mm penetrating gun using Toku Kou. In addition, the weight fo Chi-To points to a reduction of Chi-Ri weight, which has various sources contradicting each other. Of course, I’ll need to look into Chi-RI more, but something of a 2 ton reduction is not out of question.
I’ll be continuing my Japanese research as I can, to ensure that a distinctively historically accurate and well-balanced Japanese tree can come out. It has been my goal since I started this, and I will certainly work to keep it going.