来源:　http://ftr.wot-news.com/2013/08/31/stb-1-japanese-tier-10-medium-tank/

Author: Soukoudragon, Daigensui

Hello everyone, today we have another article from Soukoudragon, (revised by Daigensui) this time about (sort of confirmed) Japanese tier 10 tank. Enjoy!

After the culmination of many tested core components, the STB-1 was completed in 1969. The STB-1 was the first of two development phases in the development of the Type 74. Despite its technical and rather unimposing name, the first phase was an ambitious and successful creation while the second phase was largely about taking a katana to the cost of the tank while improving endurance and reliability. The STB-1 is indeed an imposing tank and would be a very competitive tier 10 tank in World of Tanks.

Historical Background

In the early 1960s, in the mists of the cold war, European, American, and Soviet tanks were progressing from the M48, T-55, and Centurion 3 class of tanks to the M60, Leopard 1, T-62 class of tanks. The incapability of Japan’s Type 61 tank to match these newer tanks prompted a heated debate. They debated over either improving the Type 61 (Type 61 Kai) or designing an entirely new tank. Whichever the decision was going to be, the key feature would be a 105mm cannon. Japanese tank engineer Kondo pointed out that not only a 105mm cannon but also mobility, target acquisition, and rate of fire must all be good for the sake of combined arms operations. In 1965, the decision was made to design an entirely new tank which launched the STB program.

Naming Convention

In the code name STB, the ST represents tank. And the B represents the Type 74 development program. So in the case of the Type 61, its code was STA. The developers actually wrote it by separating it with a hyphen like ST-A and ST-B. “Tank A” and “Tank B” if you will. But when the tank entered the hands of the testers, they removed the hyphen for whatever reason, making just STA and STB. The number that comes after is the cordial number for the prototype vehicle. So the 1 in STB-1 indicates the first prototype vehicle. The STB-2 was virtually identical to the STB-1. Both were tested at the same time. After their success, the second phase began and consisted of the STB-3, STB-4, STB-5, and STB-6 prototypes.

Development History

Prior to the 1965 decision to design an entirely new tank, some technologies which would later be used in the STB-1 were already in development independently in Japan. These were a new and stronger engine, a hydro pneumatic suspension, and a coaxial gear steering device which would improve the transfer of engine power. By March 1965, an air cooled 700 horse power class engine has been developed. Research on the hydro pneumatic suspension began as soon as the Type 61 tank was completed in 1961. Actual testing of it using a Type 60 APC prototype called the SU began in 1962.
For fire power, they opted for a license on the NATO standard Royal Ordnance 105mm cannon. The part that Japan imported for license production was only the barrel. They built their own breech, recoil system and mantlet around the cannon. The full length of the cannon, including all parts just mentioned, was 5,592mm long and the total weight was 2,800kg. The Japanese final version resembled the US M68 105mm version the most. From 1966 until 1967, firing tests were carried out. In the picture below, the end part is the breech and the segment between that and mantlet is the recoil system.

A prototype turret was completed when the 105mm cannon was mounted on it in 1966. In 1967 and 1968, aiming and turret rotation tests were carried out. A load assisting device was also introduced into the turret. This device maneuvered the rounds close to the breech of the cannon to enable the loader to reload faster.

The coaxial gear steering, hydro pneumatic suspension and the 700 horsepower class engine have started testing together on a test bed called the ST-T in March 1966. The ST-T alone weighed 21 tons but fully rigged, it weighed 35 tons. Length was 6.64m, width was 3.06m, and height was 1.95m. Top speed on roads was 51km/h. In August 1967, the 10ZF engine replaced the prototype engine. The 105mm cannon was later loaded onto the ST-T hull and conducted firing test. Finally, the prototype turret was mounted on top of the ST-T and again conducted firing test. The ST-T finished its testing by April 1969. Having run about 5,500 km, it has contributed tremendously to the STB program.

During the ST-T period, a mock-up was completed finally giving the first true look of the completed tank.

Building of the STB-1 started in April 1968 and finished in June 1969 with its twin, the STB-2 being finished in September of the same year. During the STB-1s testing period the engine it mounted, the 2200kg 750 horse power 10ZF-21WT had some reliability issues. It would later be replaced in the Type 74 with the 2220kg 720 horse power 10ZF-22WT engine. By May 1971 Engineer Kondo stated that the “STB-1/2 passed all qualifications including top speed, acceleration, and shown excellent mobility. That it had good results in accuracy, stabilization, secondary armaments, and protection. To further improve its endurance and reliability, the STB program is ready to move to the second phase.”

With phase 2 of the program, several systems have either been simplified or cut in order to increase reliability and/or to cut cost. The tank was actually very expensive so cost cutting was important. One feature cut was the remote controlled 12.7 machine gun at the top of the turret and replaced with a typical manual MG. The skinny stick poking up from the middle of the turret was a remote controlled periscope for the remote controlled MG. Before the STB-1 was built, Kondo preferred a manual MG because he argued that aiming at fast moving targets like aircraft would be impractical. However the remote controlled MG was installed in the STB-1 anyway only to be removed in the second phase.

Stats

In this section, some of the stats are actually coming from Type 74 sources however, those stats would very much happen to have been the same or extremely similar for the STB-1 otherwise they would not be listed here.

Data

Crew: 4
Full length: 9.423m
Hull length: 6.7m
Width: 3.18
Height: 2.25m
Ground Clearance (±hydro pneumatic suspension) 400mm±200mm
Track width: 550mm
Ground Pressure: 0.86kg/cm2

Weight: 38 tons
Engine: 750 HP/2200rpm Mitsubishi 10ZF-21WT
Top Speed: 53km/h
Transmission: Mitsubishi MT-57T (6 forward 1 reverse)
Horse Power per Ton: 18.95
Turret Traverse speed: 24°/sec (historically the same as Leopard 1 and M48)

Armor

Technically speaking, the armor is still classified. But there are estimations deduced from weight, dimensions, and on studies of numerous photos of shots under panels, welding points, and so on. The turret armor is the most speculative in nature.

Mantlet: Average thickness 195mm. There is no armor behind the mantlet.

Turret Front: 120mm
Turret side: 110mm
Turret rear: 60mm
Turret top: 40mm

For the side and rear turret, 100mm and 100mm is also a possibility but less realistic than the above estimation.

Front upper hull: 40 at 75° LOS 155
Front mid hull: 80mm at 65° LOS 189
Front lower hull: 80mm at 55° LOS 139
Side hull: 35mm
Rear hull: 25mm

Firepower

Primary Armament: Japanese modified Royal Ordnance 105mm L7 cannon.

APDS: British L28A1, not American M392 (all imported)
APFSDS: M735 (Starting from 1984)
HEAT: Type 91 (similar to M456)
HE: Type 75 HEP-T (Licensed M393 HEP)

The British L7A1 could penetrate 250 mm from 1,000 meters using L28A1, while the Japanese 105mm gun could only penetrate 240 mm. This means that 105mm Gun Rifled would have around 257 penetration in terms of WoT.

Ammo load and the Load Assisting Device (Type 74)

50 rounds. 28 in the front hull, 7 below the turret basket floor, 9 in the turret rear, 6 besides the load assisting device. 4 rounds can be placed into the load assisting device (LAD). With the device and the FCS, 1 shot every 4 seconds was possible. Now I am not absolutely certain if the characteristics described here are the same as what was installed in the STB-1 but chances are very high that they were in my opinion. So with that, it is a little hard to decide what to do with it in WoT. The ideal setup would be to have a rate of fire of about 15 rounds per minute for only the first four shots and then afterwards, have the option for the loader in the tank to either continue loading the main cannon the regular way which would be the typical RoF or to have him refill the LAD which would take whatever amount of time that would take. Also, during idle time, the loader should be able to refill the LAD.

So this 4 round “burst” (for lack of a better word) it is still nothing like the burst from a Batchat or a T57. It is a slow burst. To have a slow burst and then make the STB-1 reload the LAD as if it were a drum seems unfair since he should have the option to just reach behind or below for a new round if reloading the LAD was undesirable. One option if it works out balanced is to just ignore the fact that there is a LAD and have the RoF comparable to the Leopard or M48. Another option could be to take the LAD’s existence and average its effect over the RoF by bumping up the regular RoF a little bit, to like 7.5 or 8 rpm.

Gun elevation and Gun depression

Here is another riddle for WoT implementation. The gun elevation is + 9 and the gun depression is -6…in the turret alone. That does not take the hydro pneumatic suspension into account which adds another ± 6. Thus the full potential is + 15 and – 12. Again one option would be just to entirely ignore the problem if the end result is still a balanced tank. I think I can be ok with that decision in the case of the LAD but Japan specifically designed and utilized the hydro pneumatic suspension for their needs in the Japanese mountain and rice paddie filled terrain. It is very much a characteristic of the STB-1. So in short of actually adding support for a hydro pneumatic suspension (which by the way, the S-Tank will require if added) I would suggest cutting a half way deal. Naturally STB-1 would not usually run at high speeds looking down -12 degrees so it would be silly to add the full potential of the hydro pneumatic suspension to the gun arc in WoT. So make it half way. Half of 6 is 3. So I would suggest +12 and -9 for WoT.

In World of Tanks

Compared to the other tier 10 medium tanks in the game, the STB-1 would seem like it would feature very good maneuverability and acceleration. The leopard would still maintain its top speed advantage. The 105mm cannon combined with potentially a slightly higher RoF may give the STB-1 the highest DPS out of all tier 10 mediums. The hull armor would probably have some bounce potential at certain angles. The turret is also well angled including the thick mantlet. I would expect the turret to have some bounce potential too however the T-62a would still maintain its advantage in turret armor. One more advantage to the STB-1 is its small size, slightly smaller than the T-62a overall. The STB-1 seems like it would be a very well-rounded and competitive medium tank.

Sources:

1.戦後日本の戦車開発史　林磐男 “Post-War Japanese Tank Development History” Iwa Hayashi
2. グランドパワー “Ground Power” June 2007
3. グランドパワー “Ground Power” August 2007
4. 戦後の日本戦車 特別冊　“Postwar Japanese Tanks” Special edition September 2009
5. パンツアー “Panzer” February 2004