[WT] Type61 MBT

   Upon the request of many to see the end tier tank game Gaijin is going to give to you all in the Japanese Ground Forces patch, they recently previewed a tank known to many as Japan's first main battle tank. I would have posted this article sooner, but due to health issues and me simply procrastinating it'd been held off until now. I'll make an article dedicated to the Type61 along at a later time. But here today we will get a closer look at the first mass produced medium tank of post-war Japan, the Type 61.

Up until 1954, Japan had been barred from any military action within its own borders that was not supervised by the United States. All of the tank industry Japan had during the war had been completely shattered by the time of the Empire's collapse in 1945, and left the nation at an all time low for all military production. It was not until the creation of the Japanese Self Defense Force that Japan could start building its own military force independent of American jurisdiction. This decision was agreed upon by the two countries as tensions in the East started to accelerate with the Korean conflict growing more intense. Japan knew it needed a armoured force in case it would need to defend itself from potential Soviet actions. The arsenal at the time of the forming of the SDF only made up a small number of increasingly obsolete American tanks such as the Chaffee and Sherman. Both were deemed too outdated and complex to use extensively in Japan.

Statistics of the fourth prototype as compared
to American tanks.

Japan sought to use the American Patton tank series for influence in designing their own tank. The American built 90mm was heavily desired by Japan for use on any potential tank. However the weight of the M47 and M48 tanks was too heavy to base their own tank off of. Japan's terrain required a lightweight and small vehicle which could be easily transported through Japan’s many rail tunnels. The M47 and M48 were too large for this. Instead, the United States gave Japan permission to design their own 90mm anti tank gun, as they refused to give the license to the nation. The tank project began in 1955 with the envisionment of a light tank, however by the time the first prototypes were completed in the December of 1956, the design had evolved into a medium tank. From then until 1960 the tank project would include a total of 4 prototype designs, each unique in their own fashion. The first two medium tanks were constructed under the names ST-A1 and ST-A2. However, after the tests proved unsuccessful in the end, the ST-A2 prototype was chosen to extend design changes to meet the Ground Staff Office's requirements. 

ST-A4 Prototype.

Initially, the prototype tanks introduced a two stage torque converter manufactured by Sweden 's SRM company, however a problem in power loss and mobility proved to be unsatisfactory for the Ground Staff Office. The next two series of the prototype line were to fix this issue, however it took until 1959 for the ST-A4 prototype to be completed, another year afterwards for the ST-A3. The second stage of the tank prototype series focused on polishing the ST-A2. The changes made in these later models included a design change for the 90mm gun's muzzle break, an increase of the engine’s output, and an increase in quality of the tank shells used with the first generation 90mm. Added to this, with the ST-A3 prototype, Japan tested a new system of a remote controlled 20mm cannon located above the turret accompanied by an autoloading mechanism for the main cannon. This proved to be too expensive for Japan to justify the improvements, and the prototype ended up being canceled in favor of the more practical and simple ST-A4. The ST-A4 was later accepted for completion and after minor changes such as engine enhancements and the removal of the remote-controlled 20mm cannon in favor of a crew-served heavy machine gun, the tank was designated the Type61 Main Battle Tank.

The Type61 production model. 

  The Type 61 proved to be Japan's first post war tank produced on a large scale. However, the tank was already outdated by the time it entered widespread service, with design and mechanical flaws. Due to conflicting requirements issued by the Ground Staff Office, the tank had bounced back and forth between specifications, lengthening the development process. Moving between a series of different weight requirements and levels of gun caliber, armour, speed, and dimensions crippled the tank throughout its development, and this was reflected in the series production model. The tank proved to even be more expensive than what it was worth, and not long after its introduction was it decided to develop a new tank that would surpass the Type 61 and its flawed development history. The crew compartment was arranged so that the driver of the Type 61 was located on the right side, which was done to abide by the traffic laws of the period. This caused the 3 crew (of the 4) to have been unevenly distributed throughout the right side of the vehicle.

One of the largest flaws of the Type 61 was its overall armour protection. The tank had to keep a low armor thickness in order to reduce the weight of the chassis. The tank's hull was inclined at 30 degrees from the horizontal, with welded construction, allowing for the effective thickness to reach 90mm. The turret was casted into a bowl-like shape and was kept to 40mm on the sides, with a slope of only 80 degrees, offering  80mm thickness in theory. The result was that the Type 61’s armor protection was inferior to most other tanks of the period; Japan had only taken into consideration the T-34-85, as that had been the major opponent in the Korean war. The Type 61 in the end was only protected against basic infantry anti tank weaponry, and was incapable of defeating dedicated anti-armor projectiles from most of its probable opponents.

Armour layout of the Type61 Main Battle Tank. 

The mobility of the Type 61 did not make up for the low thickness of the tank's armour. The tank was given a modified version of the Mitsubishi 20WT engine, a 4-stroke 90 ° V 12-cylinder direct injection air-cooled diesel engine, supercharged by two turbochargers, with a displacement of 29.6 liters and a maximum output of 604 hp. This was changed into a 12 cylinder air-cooled turbocharged diesel with an output of 570hp at 2100rpm (650hp without cooling device and air purifier) and a maximum shaft torque of 200 kg/m. Designed to power a lighter vehicle, this modified engine ended up having detrimental effects on the Type 61’s performance. On roads the tank had a top speed of 55kph. Off road, the tank kept a stable 45kmh. The tracks of the tank were 500mm in width, and afforded the Type 61 a 10 meter turn radius. The minimum fuel consumption rate at full load was 210 g / PSh. The main tank is 450 liters, and the auxiliary tank is 200 liters.  The acceleration performance of the Type 61 was 0 to 200 meters in 25 seconds. While this may seem fast for an armored vehicle, the numbers should be measured against those of the third generation tanks of other countries which were deployed later, as the Japanese Defense Agency did. For instance, the Leopard 2A4 is estimated to have a time of 23.5 seconds, and the M1 Abrams' prototype XM1 Is estimated to time at 29 seconds. Both of these vehicles are significantly heavier than the Type 61, however. Considering the power weight ratio of the Type 61, the tank clearly emphasized acceleration performance rather than the maximum speed. Given the mountainous nature of Japan, this was clearly a good development decision.

Mitsubishi 12HM-21WT.

The transmission system of the Type 61 is frontally mounted, the only tank to use this transmission system since the end of WWII. As a result, the height of the vehicle could not be lowered, and part of the front armor plate of the car body became a bolt fastening panel for maintenance of the transmission, and brought accompanying flaws in the armor protection. The transmission was a double differential manual shifter with 5 forward speeds and 1 reverse. This was a departure from the earlier two prototypes of the tank, which were equipped with a two-stage torque converter manufactured by Sweden's SRM Company. however when it was installed, there were problems with power loss and agility, which was not a satisfying appearance to the Council and their requirements. Finally, after trying to emulate the automatic gearshift of the M47 and M48 Patton tanks, more complex systems were abandoned a manual gear-shifting system was chosen instead.Steering was provided by a lever for each track, as in the Sherman tanks. This made the Type 61 considerably more difficult to maneuver than the M24s and M41s originally provided to Japan by the US military.

Interior cutaway view of the Type61. 

The armament of the Type 61 was influenced by the American 90mm. The layout of the Type 61’s 90mm was kept identical, however the barrel was elongated. It used the same standard ammunition as the US 90mm.  Production rights were given to the Japan Steel Works company, with American aid in providing munitions. In accordance to the Defense Agency's file of the gun, XB3002, dated April 26 1961, the gun's barrel was made to 4730mm in length, 52 caliber, weight of 2,500kg, and a barrel weight of 1,150kg. The gun shield had weighed nearly 750kg. According to the Defense Agency's file XD9001, the maximum speed of the turret traverse was 24° per second, The depression speed of the gun being 4°  second.  The gun could also elevate to 13 degrees while having a depression of -10 degrees. The firing rate of the gun ranged from 10 to 15 rounds per minute.

The shells used on the Type61 90mm Tank Gun had been kept similar to the American counterpart, however Japan had produced them under their own conditions. The main shell used in the gun was the Japanese model of the AP-T M318A1. It had a recorded penetration of 189mm at 1000 meters. Calculations of the shell has it listed to 222mm at point blank range, and 158mm at 2000 meters. 

Weight:  19.9kg
Length:  942.6mm
Shell Weight: 11kg
Shell Length: 364mm
Output: 914m per sec.
Range: 21,031m
Pressure: 3,300kg/cm2

Secondary weapons for the Type 61 included a coaxial 7.62mm M1919A4 machine gun, with a range of 800 meters and a rate of fire of 550 rounds per minute. Located on the top of the turret was a 12.7mm M2 heavy machine gun, which had  +55 ~ -10 degree angles, a rof of 550rpm, and range of approx. 1,200 meters.  The 90mm tank shells were stowed into two locations in the tank, directly behind the gun crew in the rear turret box, and to the left and right of the turret in the hull. 

Type61 90mm Tank Gun as drawn by the Defense Agency. 

Weight: 35t
Crew: 4 men
Length 8.19  m
Height: 2.49 m (3.26 m with MG)
Width: 2.95 m
Engine: Mitsubishi 12HM-21WT.
Cylinders: V12 Air cooled Diesel (Supercharged)
Power Output: 570 hp/2,100 rpm (650 hp max)
Max Speed: 55kmh
Armament: x1 Type61 90mm Tank Gun, x1 12.7mm M2 , x1 M1919A4 MG

Gun Shield Armour:
Mantlet: 125mm
Top Front - 40mm @ 60° (90mm)
Cheeks: 90mm
Top Side - 40mm
Bottom Side - 60mm
Roof - 18mm
Rear - 35mm

Hull Armour:
Front - 45mm @ 30° (90mm)
Side - 30mm
Roof - 12mm
Rear - 25mm

Suspension:
Front - 35mm
Side - 35mm
Rear - 20mm