Today, we have another wonderful guest article from Soukoudragon (US forums) about Japanese tanks. This time, it’s about something pretty exotic: hightier Japanese light tanks.

Author: Soukoudragon

Japanese High Tier Light Tanks
Possible?

What are these STA light tanks?

The Type 61 tank was Japan’s first post-war tank. There were four prototypes to this tank. They were the ST-A1, ST-A2, ST-A3, and ST-A4. They all weighed about 35 tons. Well, the A1 and the A2 were about 34 tons.

The STA light tanks are none of the above.

What are being called the STA light tanks were the plans for Japan’s new post-war tank before the ST-A1 and ST-A2 designs that were accepted and built. The early plans called for the new tank to be light in weight.

Historical Background for the Light Weight Plans

During the Korean War, American tanks that were over 30 tons such as the M26 and M46 had difficulty in the mountainous regions and rice paddies in the Korean Peninsula whereas the Soviet-made T-34-85 of the North Koreans was able to maneuver in this environment. The terrain in Japan is very similar to the terrain in the Korean peninsula. This is why Japan decided against purchasing the heavier Patton medium tanks from the USA. The Japanese liked the M24 Chaffee since it was light and was able to move around but they needed more firepower.

One other reason why a light tank was desired was because of the French thought on tanks at the time. With the advance of HEAT munitions and the development of SS-10 anti-tank missile, heavy armor was becoming to seem like it’s time had passed.

For these reasons, at the end of January in 1955, the Ground Staff Office (GSO) submitted the goals for the new 25ton Japanese tank plan which was as follows.

Weight: 25 tons
Main armament: 90mm
Emphasis on a strong engine and low ground pressure
Best possible armor within the above requirements.

-Before this 25 ton, the plan for the tank was 20 tons with a 76 mm gun, but this changed because of the M-24 could not penetrate the T-34 during the Korean War, thus leading to the need for a 90 mm gun- (Daigensui)

There were other ideas for a new tank already around. According to the Chief engineer from GSO of the STA project (Kondo Kiyohide), in September 1953, plans were to have a tank that can perform infantry support as well as play the armored force role. It would need to be able to run along the edges of waterlines, through beach sand, and pass through rice paddies with ease. From the beginning, it was decided to sacrifice armor. It would make up for the lack of armor by using the terrain to its advantage in off-road areas, low vehicle height, good gun depression, and emphasis on torque instead of high speed. It was also to be easily transportable on rail lines.

STA Tank Project Development Begins

Development started in June 1955 under the Defense Agency order #12. Kondo describes the order as the following.
In Showa year 30 (1955) first 2 prototypes are to be built and then increased to 5 prototypes by the end of the year. Contracted companies are Mitsubishi Heavy Industries and Japan Steel Works.

Upon reflection on progress thus far, in May 1955, GSO put together a new list of primary requirements as a 30 ton plan which are as follows.

-The change from 25 tons to 30 tons is due to the premise that with the development of bazookas and anti-tank missiles 25 tons would not be able to accommodate enough armor- (Daigensui)

Crew: 4
Full weight: Under 30 tons
Length: about 6.0m
Height: under 2.8m
Width: about 2.0m
Ground clearance: 0.40m
Main armament: 90mm
Gun depression: -15
Rounds: 50
Secondary weapon: 7.62 MGx1
Engine type: Diesel air-cooled
Horse Power: 600hp
Horse Power per ton: 20hp/ton
Top speed: 50km/h
Wading depth: over 1.2m
Drive type: Rear wheel drive desired
Steering type: Hydraulic desired
Ground pressure: 0.8kg/cm2
Rangefinder: Yes
Infrared vision: Yes

Kondo and the Technical Research Department (TRD) believed that these specs were wish-full thinking. So a development council was held between several organizations. They included TRD, GSO, Defense Agency Bureau Weapons Division, and the Procurement Head Office. Former Lieutenant General Hara Tomio and other experienced tank developers and tank users also participated in the development council. In addition to the development council, TRD consulted with Japan Weapons Industry Group (JWIG). This consultation was open to joining the makers together and also wartime experienced military men.

From that meeting with JWIG, a compromise plan was made. It called for two tank designs. A 20~25 ton tank armed with a 76mm cannon and a 25~30 ton tank armed with a 90mm cannon. It was analogous to the concept Germany had in having a Panzer III (37mm) and a Panzer IV (75mm) to complement each other. The 20-25 ton tank reflected GSO’s plan to have a light tank that can easily traverse the terrain of Japan and be easy to transport. And the 25~30 ton tank reflected Kondo and TRD’s plan for firepower and some armor (somewhat contrary to the 1953 description regarding armor).

However according to Kondo, some internal ministers have leaked their intention to give a 30 ton tank design a chance in performing the kind scouting that the M24 Chaffee was capable of doing.

According to Sone Masanori in 1980, the people that were deeply rooted in the 25 ton concept still felt that it should have been a 25 ton tank made instead. In 1964, at an investigation on the situation of European tank development, Kaihara stated that the 36 ton Type 61 destroyed the vision for a 25 ton tank.

In 1954, the same year when GSO gave its 25 ton tank plan, Japan entered into the U.S. and Japan Mutual Defense Assistance Agreement. This meant that there would be technology transfers from the US to Japan including a loan of the 90mm mounted M36 Jackson. If a Sherman based tank was to mount the 90mm cannon, in order for the vehicle to handle the weapon, the weight would need to rise to about 31 tons. This fact made most in the Japanese Ground Self Defense Force (JGSDF) feel that a 25 ton design was unlikely.

Leading up to the mock-ups and two Experimental ST-A tanks

In the mist of the 25 ton clash, in August 1955, Kondo transferred from the GSO to the TRD and assumed head position of the STA program. This marks the end of the 25 ton plan as well as the compromise plan of the 20~25 ton and 25~30 ton tank duo.

Kondo stated that the starting point in designing the tank was to be able to handle the shock from firing. This tank was to be different than an SPG. This tank will not always have to option to select where to shoot from. It needs to be ready to shoot whether it is moving, in the snow, on a slope, or shooting off from its side. It needs to be able to do that on a moment’s notice and without slipping. In addition to that, the vehicle needs to maintain accuracy and high rate of fire by providing a stable platform that quickly stops shaking after shooting.

From the above came the 32 ton plan. Anything heavier would break the plan to have 20 horsepower per ton.

GSO questioned on how the 32 ton plan was supposed to be easily transportable. The response to that was that on the current Japanese trains, the maximum weight limit for open freight cars was 35 tons. Long lumber materials were crammed on such freight up to 35 tons. Therefore all crew, fuel and ammunition would have to be removed for transportation.

In October, TRD presented the 32 ton plan mock up (model 1) while GSO presented a 35 ton plan mock up ([model II] which is contrary to their earlier 25 ton plan) at the 5th development council. The only main difference between the two mock ups was the thickness of the armor which the thickness is unidentified in my source.

This is a picture of the 32 ton mock up made by the Technical Research Department. The turret-less vehicle in the back is the hull of a M36 Jackson.

Both were seen as having thin armor so when it was time to move on to building the tank, a low profile version was ordered which becomes the ST-A1. The ST-A2 would be closer to as it is in the mock up.

Translation Glossary

Because I am not absolutely sure if I translated some of the official organizational names or the names of people correctly in this article, they are all listed here alongside the correct Japanese names for cross-language reference purposes.

People
曽根正儀 Sone Masanori
原乙未生 Hara no Tomio
近藤清秀 Kondo Kiyohide

Organizations/meetings
陸上幕僚監部　Ground Staff Office (GSO)
技術研究所 Technical Research Department (TRD)
防衛庁内局武器課Defense Agency Bureau Weapons Division
調達実施本部Procurement Head Office
装備審議会 Development Council
日本兵器工業会　Japan Weapons Industry Group (JWIG)
陸上自衛隊 Japanese Ground Self Defense Force (JGSDF)

Source:
Ground Power (グランドパワー) March 2008 edition pages 18-25
WOT NA Japanese Tank Tree & Guns Discussion poster: Daigensui

Implementation into WoT

Assuming the OK is giving, here is an option for implementation.

Tier 6 STA JWIG I
Tier 7 STA JWIG II

These two tanks are coming from the compromise plan by JWIG. The 25 ton plan often pushed by GSO as well as GSO’s proposed 30 ton plan seems to have not been well defined and after consultation with practically all tank experts in Japan, the compromise plan came out. So I think it makes most sense to use the compromise plan instead of GSO’s plans.

About the naming convention I gave, the compromise plan did not give a simple (at least not in my source) sort of “20 ton plan” or a “25 ton plan.” If I was to use “20 ton plan” and “25 ton plan” the 25 ton plan could get confused with GSO’s 25 ton plan. Also, since there is no specific naming of a ton in the plan name, I opted to use a cordial number “I” and “II” method. Since “STA I” and “STA II” could also perhaps be confusing with the ST-A1 and the ST-A2, I put in the acronym JWIG.

So what do we have for creating these tanks?

First the guns…

Quite simply, the guns are from the USA. Japan was dependent on receiving some combat vehicles from the USA until the Self Defense Force was created but even with that, there would be a lot of technology transfers via the U.S. and Japan Mutual Defense Assistance Agreement which was signed in March 8 1954, before the JWIG meeting. The M24 Chaffee was giving to Japan in 1952, before the start of the STA program. So the Tier 6 STA JWIG I can have the US M6 75mm cannon as a stock gun. Japan also had about 250 M4A3(76)W HVSS Shermans which were phased out when the Type 61 entered service. So the M1 76mm cannon can be the top gun which matches the compromise plan’s call for a 76mm cannon.

The stock gun on Tier 7 STA JWIG II can be the 76mm cannon. Due to its heavier weight, it would make for a better firing platform as was planned and thus gains access to the 90mm cannon. The first 90mm cannon would be from the M36 loaned to Japan. The next 90mm cannon would be the Type 61 90mm cannon. Going by what Kondo describes about accuracy and RoF, the 90mm cannons on the STA JWIG II would have less accuracy and a lower RoF than the medium STA/Type 61 tanks.

For both the I and II, by maintaining the same hull as it is on the 32 ton mockup which is very similar to the ST-A2, the giving similar size area for the engine compartment gives access to the Japanese Post-War engines for the Type 61. With the lighter hulls, that will give the necessary hp/ton for the STA lights. High hp/ton was described in early Japanese demands for the tank so this configuration reflects some historical backing.

Name: Mitsubishi DL10T
Power: 500 hp
Type: Diesel
Weight: 2,200 kg
Compatibility: STA-1/STA-2

Name: Mitsubishi 12HM20WT
Power: 570 hp
Type: Diesel
Weight: 2,400 kg
Compatibility: STA-1~4

Name: Mitsubishi 12HM21WT
Power: 604/650 hp (maximum/naked shaft output without cooling device)
Type: Diesel
Weight: 2,400 kg
Compatibility: Type 61

(Engine list by Daigensui)

Using this hull would also preserve the historical demand for good gun depression.

Other characteristics such as the tracks and turret can be borrowed from the ST-A1 and the ST-A2. Just the turret would have less armor.