Compared to the most well known Japanese fighter of World War 2, the A6M “Zero”, the J2M Raiden (“Jack”) was both less famous and less numerous. More than 10,000 A6Ms were built, but barely more than 600 J2Ms were built. Still, the J2M is a noteworthy aircraft. Despite being operated by the Imperial Japanese Navy (IJN), it was a strictly land-based aircraft. The Zero was designed with a lightweight structure, to give extreme range and maneuverability. While it had a comparatively large fuel tank, it was lightly armed, and had virtually no armor. While the J2M was also very lightly built, it was designed that way to meet a completely different set of requirements; those of a short-range interceptor. The J2M's design led to it being one of the fastest climbing piston-engine aircraft in World War 2, even though its four 20mm cannons made it much more heavily armed than most Japanese planes.
Development of the J2M began in October 1938, under the direction of Jiro Hirokoshi, in response to the issuance of the 14-shi interceptor requirement (1). Hirokoshi had also designed the A6M, which first flew in April 1939. However, development was slow, and the J2M would not make its first flight until 20 March 1942, nearly 3 ½ years later (2). Initially, this was due to Mitsubishi's focus on the A6M, which was further along in development, and of vital importance to the IJN's carrier force. Additionally, the J2M was designed to use a more powerful engine than other Japanese fighters. The first aircraft, designated J2M1, was powered by an MK4C Kasei 13 radial engine, producing 1430 horsepower from 14 cylinders (3) (compare to 940 horsepower for the A6M2) and driving a three bladed propeller. The use of such a powerful engine was driven by the need for a high climb rate, in order to fulfill the requirements set forth in the 14-shi specification.
The climb rate of an aircraft is driven by specific excess power; by climbing an aircraft is gaining potential energy, which requires power to generate. Specific Excess Power is given by the following equation;
It is clear from this equation that weight and drag must be minimized, while thrust and airspeed are maximized. The J2M was designed using the most powerful engine then available, to maximize thrust. Moreover, the engine was fitted with a long cowling, with the propeller on an extension shaft, also to minimize drag. In a more radical departure from traditional Japanese fighter design (as exemplified by aircraft such as the A6M and Ki-43), the J2M had comparatively short, stubby wings, only 10.8 m wide on the J2M3 variant, with a relatively high wing loading of 1.59 kN/m2 (33.29 lb/ft2) (2). (It should be noted that this wing loading is still lower than contemporary American aircraft such as the F6F Hellcat. The small wings reduced drag, and also reduced weight. More weight was saved by limiting the J2M's internal fuel, the J2M3 had only 550 liters of internal fuel (2).
Hirokoshi did add some weight back into the J2M's design. 8 millimeters of steel armor plate protected the pilot, a luxurious amount of protection compared to the Zero. And while the J2M1 was armed with the same armament as the A6M (two 7.7mm machine guns and two Type 99 Model 2 20mm cannons), later variants would be more heavily armed, with the 7.7mm machine guns deleted in favor of an additional pair of 20mm cannons. Doubtlessly, this was driven by Japanese wartime experience; 7.7mm rounds were insufficient to deal with strongly built Grumman fighters, let alone a target like the B-17.
The first flight of the J2M Raiden was on March 20th, 1942. Immediately, several issues were identified. One design flaw pointed out quickly was that the cockpit design on the J2M1, coupled with the long cowling, severely restricted visibility. (This issue had been identified by an IJN pilot viewing a mockup of the J2M back in December 1940 (1).) The landing speed was also criticized for being too high; while the poor visibility over the nose exacerbated this issue, pilots transitioning from the Zero would be expected to criticize the handling of a stubby interceptor.
Wrecked J2M in the Philippines in 1945. The cooling fan is highly visible.
However, the biggest flaw the J2M1 had was poor reliability. The MK4C engine was not delivering the expected performance, and the propeller pitch control was unreliable, failing multiple times. (1) As a result, the J2M1 failed to meet the performance set forth in the 14-shi specification, achieving a top speed of only 577 kph, well short of the 600 kph required. Naturally, the climb rate suffered as well. Only a few J2M1s were built.
The next version, the J2M2, had several improvements. The engine was updated to the MK4R-A (3); this engine featured a methanol injection system, enabling it to produce up to 1,800 horsepower for short periods. The propeller was switched for a four blade unit. The extension shaft in the J2M1 had proved unreliable, in the J2M2 the cowling was shortened slightly, and a cooling fan was fitted at the the front. These modifications made the MK4R-A more reliable than the previous engine, despite the increase in power.
However, there were still problems; significant vibrations occurred at certain altitudes and speeds; stiffening the engine mounts and propeller blades reduced these issues, but they were never fully solved (1). Another significant design flaw was identified in the summer of 1943; the shock absorber on the tail wheel could jam the elevator controls when the tailwheel retracted, making the aircraft virtually uncontrollable. This design flaw led to the death of one IJN pilot, and nearly killed two more (1). Ultimately, the IJN would not put the J2M2 into service until December 1943, 21 months after the first flight of the J2M1. 155 J2M2s would be built by Mitsubishi (3).
By the time the J2M2 was entering service, the J2M3 was well into testing. The J2M3 was the most common variant of the Raiden, 260 were produced at Mitsubishi's factories (3). It was also the first variant to feature an armament of four 20mm cannons (oddly, of two different types of cannon with significantly different ballistics (2); the 7.7mm machine guns were replace with two Type 99 Model 1 cannons). Naturally, the performance of the J2M3 suffered slightly with the heavier armament, but it still retained its excellent rate of climb. The Raiden's excellent rate of climb was what kept it from being cancelled as higher performance aircraft like the N1K1-J Shiden came into service.
The J2M's was designed to achieve a high climb rate, necessary for its intended role as an interceptor. The designers were successful; the J2M3, even with four 20mm cannons, was capable of climbing at 4650 feet per minute (1420 feet per minute) (2). Many fighters of World War 2, such as the CW-21, were claimed to be capable of climbing 'a mile a minute', but the Raiden was one of the few piston-engine aircraft that came close to achieving that mark. In fact, the Raiden climbed nearly as fast as the F8F Bearcat, despite being nearly three years older. Additionally, the J2M could continue to climb at high speeds for long periods; the J2M2 needed roughly 10 minutes to reach 30000 feet (9100 meters) (4), and on emergency power (using the methanol injection system), could maintain a climb rate in excess of 3000 feet per minute up to about 20000 feet (about 6000 meters).
Analysis in Source (2) shows that the J2M3 was superior in several ways to one of its most common opponents, the F6F Hellcat. Though the Hellcat was faster at lower altitudes, the Raiden was equal at 6000 meters (about 20000 feet), and above that rapidly gained superiority. Additionally, the Raiden, despite not being designed for maneuverability, still had a lower stall speed than the Hellcat, and could turn tighter. The J2M3 actually had a lower wing loading than the American plane, and had flaps that could be used in combat to expand the wing area at will. As shown in the (poorly scanned) graphs on page 39 of (2), the J2M possessed a superior instantaneous turn capability to the F6F at all speeds. However, at high speeds the sustained turn capability of the American plane was superior (page 41 of (2)).
The main area the American plane had the advantage was at high speeds and low altitudes; with the more powerful R-2800, the F6F could more easily overcome drag than the J2M. The F6F, as well as most other American planes, were also more solidly built than the J2M. The J2M also remained plagued by reliability issues throughout its service life.
In addition to the J2M2 and J2M3 which made up the majority of Raidens built, there were a few other variants. The J2M4 was fitted with a turbo-supercharger, allowing its engine to produce significantly more power at high altitudes (1). However, this arrangement was highly unreliable, and let to only two J2M4s being built. Some sources also report that the J2M4 had two obliquely firing 20mm Type 99 Model 2 cannons in the fuselage behind the pilot (3). The J2M5 used a three stage mechanical supercharger, which proved more reliable than the turbo-supercharger, and still gave significant performance increases at altitude. Production of the J2M5 began at Koza 21st Naval Air Depot in late 1944 (6), but ultimately only about 34 would be built (3). The J2M6 was developed before the J2M4 and J2M6, it had minor updates such as an improved bubble canopy, only one was built (3). Finally, there was the J2M7, which was planned to use the same engine as the J2M5, with the improvements of the J2M6 incorporated. Few, if any, of this variant were built (3).
A total of 621 J2Ms were built, mostly by Mitsubishi, which produced 473 airframes (5). However, 128 aircraft (about 1/5th of total production), were built at the Koza 21st Naval Air Depot (6). In addition to the reliability issues which delayed the introduction of the J2M, production was also hindered by American bombing, especially in 1945. For example, Appendix G of (5) shows that 270 J2Ms were ordered in 1945, but only 116 were produced in reality. (Unfortunately, sources (5) and (6) do not distinguish between different variants in their production figures.)
Though the J2M2 variant first flew in October 1942, initial production of the Raiden was very slow. In the whole of 1942, only 13 airframes were produced (5). This included the three J2M1 prototypes. 90 airframes were produced in 1943, a significant increase over the year before, but still far less than had been ordered (5), and negligible compared to the production of American types. Production was highest in the spring and summer of 1944 (5), before falling off in late 1944 and 1945.
The initial J2M1 and J2M2 variants were armed with a pair of Type 97 7.7mm machine guns, and two Type 99 Model 2 20mm cannons. The Type 97 used a 7.7x56mm rimmed cartridge; a clone of the .303 British round (7). This was the same machine gun used on other IJN fighters such as the A5M and A6M. The Type 99 Model 2 20mm cannon was a clone of the Swiss Oerlikon FF L (7), and used a 20x101mm cartridge.
The J2M3 and further variants replaced the Type 97 machine guns with a pair of Type 99 Model 1 20mm cannons. These cannons, derived from the Oerlikon FF, used a 20x72mm cartridge (7), firing a round with roughly the same weight as the one used in the Model 2 at much lower velocity (2000 feet per second vs. 2500 feet per second (3), some sources (7) report an even lower velocity for the Type 99). The advantage the Model 1 had was lightness; it weighed only 26 kilograms vs. 34 kilograms for the model 2. Personally, I am doubtful that saving 16 kilograms was worth the difficulty of trying to use two weapons with different ballistics at the same time. Some variants (J2M3a, J2M5a) had four Model 2 20mm cannons (3), but they seem to be in the minority.
In addition to autocannons and machine guns, the J2M was also fitted with two hardpoints which small bombs or rockets could be attached to (3) (4). Given the Raiden's role as an interceptor, and the small capacity of the hardpoints (roughly 60 kilograms) (3), it is highly unlikely that the J2M was ever substantially used as a bomber. Instead, it is more likely that the hardpoints on the J2M were used as mounting points for large air to air rockets, to be used to break up bomber formations, or ensure the destruction of a large aircraft like the B-29 in one hit. The most likely candidate for the J2M's rocket armament was the Type 3 No. 6 Mark 27 Bomb (Rocket) Model 1. Weighing 145 pounds (65.8 kilograms) (8), the Mark 27 was filled with payload of 5.5 pounds of incendiary fragments; upon launch it would accelerate to high subsonic speeds, before detonating after a set time (8). It is also possible that the similar Type 3 No. 1 Mark 28 could have been used; this was similar to the Mark 27, but much smaller, with a total weight of only 19.8 pounds (9 kilograms).
The first unit to use the J2M in combat was the 381st Kokutai (1). Forming in October 1943, the unit at first operated Zeros, though gradually it filled with J2M2s through 1944. Even at this point, there were still problems with the Raiden's reliability. On January 30th, a Japanese pilot died when his J2M simply disintegrated during a training flight. By March 1944, the unit had been dispatched to Balikpapan, in Borneo, to defend the vital oil fields and refineries there. But due to the issues with the J2M, it used only Zeros. The first Raidens did not arrive until September 1944 (1). Reportedly, it made its debut on September 30th, when a mixed group of J2Ms and A6Ms intercepted a formation of B-24s attacking the Balikpapan refineries. The J2Ms did well for a few days, until escorting P-47s and P-38s arrived. Some 381st Raidens were also used in defense of Manila, in the Phillipines, as the Americans retook the islands. (9) By 1945, all units were ordered to return to Japan to defend against B-29s and the coming invasion. The 381st's J2Ms never made it to Japan; some ended up in Singapore, where they were found by the British (1).
least three units operated the J2M in defense of the home islands of Japan; the 302nd, 332nd, and 352nd Kokutai. The 302nd's attempted combat debut came on November 1st, 1944, when a lone F-13 (reconaissance B-29) overflew Tokyo (1). The J2Ms, along with some Zeros and other fighters, did not manage to intercept the high flying bomber. The first successful attack against the B-29s came on December 3rd, when the 302nd shot down three B-29s. Later that month the 332nd first engaged B-29s attacking the Mitsubishi plant on December 22nd, shooting down one. (1)
The 352nd operated in Western Japan, against B-29s flying out of China in late 1944 and early 1945. At first, despite severe maintenace issues, they achieved some successes, such as on November 21st, when a formation of B-29s flying at 25,000 feet was intercepted. Three B-29s were shot down, and more damaged.
In general, when the Raidens were able to get to high altitude and attack the B-29s from above, they were relatively successful. This was particularly true when the J2Ms were assigned to intercept B-29 raids over Kyushu, which were flown at altitudes as low as 16,000 feet (1). The J2M also had virtually no capability to intercept aircraft at night, which made them essentially useless against LeMay's incendiary raids on Japanese cities. Finally the arrival of P-51s in April 1945 put the Raidens at a severe disadvantage; the P-51 was equal to or superior to the J2M in almost all respects, and by 1945 the Americans had much better trained pilots and better maintained machines. The last combat usage of the Raiden was on the morning of August 15th. The 302nd's Raidens and several Zeros engaged several Hellcats from VF-88 engaged in strafing runs. Reportedly four Hellcats were shot down, for the loss of two Raidens and at least one Zero(1). Japan surrendered only hours later.
At least five J2Ms survived the war, though only one intact Raiden exists today. Two of the J2Ms were captured near Manila on February 20th, 1945 (9) (10). One of them was used for testing; but only briefly. On its second flight in American hands, an oil line in the engine failed, forcing it to land. The aircraft was later destroyed in a ground collision with a B-25 (9). Two more were found by the British in Singapore (1), and were flown in early 1946 but ex-IJN personnel (under close British supervision). The last Raiden was captured in Japan in 1945, and transported to the US. At some point, it ended up in a park in Los Angeles, before being restored to static display at the Planes of Fame museum in California.
F6F-5 vs. J2M3 Comparison
An additional two dozen Raiden photos: https://www.worldwarphotos.info/gallery/japan/aircrafts/j2m-raiden/
All photos were taken by myself in year 2016 during my visit to Beijing. Tanks are from the Military Museum of the Chinese People's Revolution and the Tank Museum(currently closed). Enjoy.
No.1: Type 94 Light armored car (Tankette) in the Tank Museum
This is the early version of the Type 94 Tankette. It was found in a river in 1970s. It is the best preserved Type 94 Tankette in the world.
No.2: Type 97 Medium Tank in the Tank Museum
This is a late version Type 97 medium tank. It carries the old small 57mm gun turret but has the revised engine ventilation port. This tank was donated by the Soviet 7th mechanized division before they withdrew from China in 1955.
No.3: Type 97 Medium Tank Kai in the Military Museum of the Chinese People's Revolution
This Type 97 Medium Tank Kai's combat serial number is 102. It belonged to the former China North-East tank regiment. It took part in the attack of Jinzhou against KMT army on 1948-9-14, and did great contribution for knocking out their bunkers and MG nests by shooting and ramming. Thus after the battle this tank was awarded with an honored name:"The Hero(功臣号)“ About the tank itself, it was assembled by the Chinese army themselves by using destroyed or damaged Chi-Ha parts after the surrender of Japan. This particular tank was built up with a normal Type 97's chassis(57mm gun version) early model, and a Type 97 Kai's Shinhoto(New turret for the 47mm gun). However there are other saying claim that this tank was modified by the Japanese. It was the first tank that roared over the Tiananmen Square during the Founding Ceremony of China on 1949-10-1.
The same tank on 1949-10-1. China's tank army origins from old IJA tanks.
No.4: Type 97 Medium Tank in the Military Museum of the Chinese People's Revolution
Sorry, only one photo was taken. This Type 97 Medium Tank has a chassis from Type 97 Medium Tank Kai and a turret from a normal Type 97 Medium Tank. It was merged together by the Chinese army.
No.5: Type 95 Armored Track(Train track) Vehicle in the Military Museum of the Chinese People's Revolution
Only two samples survived. One is in China here and one is in Kubinka, Russia (Maybe now it is transfered to the Patriot Park? I don't know).
Hope you enjoy the photos I took! No repost to other places without my permission.
This is an article simply to show you guys here how Waffentrager is a faker. The original article ( https://www.weibo.com/ttarticle/p/show?id=2309404213101531682050) was written in Chinese and Japanese. For better understanding I will translate and edit the article and post it here.
And I must tell you why I want to reveal this shit: Long time ago I found many sayings from Waffentrager’s blog which I had never heard of, so I turned to my Japanese friend and IJA tank researcher Mr.Taki and asked him to confirm a few of them. In the end it turned out that none of Waffentrager’s article is true. I once argued with him and he not only failed to give out his reference but also deleted my replies! I’m very angry!
Now let’s get started.
At the very beginning I recommend all of you who opened this post to take a look at Waffentrager’s original article, that will help you understand what I’m debating.
Here is the link to the original article: https://sensha-manual.blogspot.jp/2017/09/the-ho-ri-tank-destroyer.html?m=0
In China we need to use VPN(aka “ladder-梯子” or “the scientific way of browsing the Internet-科学上网” in Chinese)to open that link above so at first I post out Waffentrager’s original post in the form of screenshots in my article. I’ll skip that here.
Fig.1: I will skip his original article.
Now, I had raised my first question here: Please take a look at the screenshot:
Fig.2: My first question
In the original article, Waffentrager insisted that the Type 5 gun tank was built in July, 1944 and fully assembled in August. It was also put into trials at the same time.
Fig.3: Waffentrager’s original article.
But, is that true? Let’s have a look at the Japanese archive:
Important Fig.4: Archive code C14011075200, Item 4
Notice the part with the red, this is the research and develop plan for the Japanese Tech Research center in 1943, and had been edited in 1944. ◎砲１００(Gun-100) is the project name for the 105mm gun used by Type 5 gun tank. The column under it says: “Research a tank gun with 105mm caliber and a muzzle velocity of 900m/s”. This means that the gun had just begun to be developed and from the bottom column we can know that it was PLANNED to be finished in 1945-3[完成豫定 means ”plan to be finished” and 昭２０、３ means ”Shouwa 20-3”. Shouwa 20 is 1945 in Japan (you can wiki the way for Japanese to count years I’m not going to explain it here)]
Next let’s move on to the Type 5 gun tank itself, here is the Japanese archive:
Important Fig.5: Archive code C14011075200, Item 7
“新砲戦車(甲)ホリ車” is the very very first name of Type 5 gun tank, it should be translated into:”New gun tank(A), Ho-Ri vehicle”. “ホリ” is the secret name of it. Still from the column we can easily know that Ho-Ri was also planned to be finished in 1945-3. But under that column there is another one called:”摘要(Summary or outline)”, in this it says:”砲１００、第一次試作完了昭和１９、８”, In English it is: “Gun-100, First experimental construction(prototype construction) finished in Shouwa 19-8(1944-8)” What does it mean? It means that in 1944-8, Only the 105mm gun used by the Type 5 gun tank was finished! If the Ho-Ri tank itself was finished why it was not in the 摘要 column? So how could an unfinished tank mounted the prototype gun? Waffentrager is talking bullshit.
Also from Mr.Kunimoto’s book, he gave the complete schedule of the 105mm gun, here it is:
Important Fig.6: Kunimoto’s schedule
“修正機能試験” means ”Mechanical correctional test”, it took place in 1944-8, this matches the original Japanese archive(though this chart was also made from original archives). At that time the gun had just finished, not the tank.
Next is this paragraph from Waffentrager’s article:
Fig.7: Weighing 35 tons
From the archive above(important Fig.5) we can learn from the second large column”研究要項(Research items)” that Ho-Ri was only PLANNED to be 35 tons, and maximum armour thickness was PLANNED to be 120mm, not was. Waffentrager is lying, he used the PLANNED data as the BUILT data. I will post out the correct data below later to see what Ho-Ri is really like when its design was finished.
Fig.8: 全備重量-約三五屯(Combat weight-app.35t), 装甲(最厚部)-約一二〇粍(Armour, thickest part-app.120mm)
At this time, some of the people might inquire me that:”Maybe the Type 5 gun tanks were really finished! You just don’t know!” Well, I will use the archives and books to tell these guys that they are totally wrong. None of the Type 5 gun tank was finished.
Always let’s look at Waffentrager’s article first. He said that a total of 5 Ho-Ri were completed.
Fig.9: Waffentrager said 5 Ho-Ri were completed.
He also put an original Japanese archive(C13120839500) to “enhance” his “facts”.
Fig.10: Waffentrager’s archive
Everyone can see the”ホリ車,1-3-1” in the document, and someone might actually believe that 5 Ho-Ri were actually built. But they are wrong! Waffentrager is cheating you with “only a part of the original document”! Here is what the original archive really looks like:
Important Fig.11: Archive code C13120839500, Item 7
“整備計画” is “Maintenance plan” in English, again it was PLAN! The whole plan was made in 1944-12-26. I don’t actually know how Waffentrager can misunderstand this, maybe he doesn’t even know Japanese or Chinese!
Important Fig.12: The cover of the same archive, “昭和十九年十二月二十六日” is 1944-12-26” in English.
I have other archives to prove that Ho-Ri were not finished as well:
Important Fig. 13 and 14: Mitsubishi’s tank production chart made by the American survey team after the war ends.
From the chart you can only find out Type 4 and Type 5 medium tanks’ record. There is no existence of Type 5 gun tank Ho-Ri, or the”M-5 Gun Tank” in the chart’s way.
Except for the archives, many books written by Japanese also mentioned that Type 5 gun tank were not finished:
Fig.15: Kunimoto’s record.
“二〇年五月完成予定の五両の終戦時の工程進捗度は、やっと五〇パーセントであり、完成車両出せずに終戦となった。” In English it’s: “When the war ended, the five Ho-Ri planned to be finished in 1945-5 had finally reached 50% completion. No completed vehicle were made when the war ended.”
Here is another book written by Japanese with the help of former IJA tank designer, Tomio Hara:
Important Fig.16: Tomio Hara’s book
“完成をみるには至らなかった” Again he emphasized that the tank was not finished. Also when Ho-Ri’s design was finished its combat weight was raised to 40 tons, not the planned 35 tons. It was only powered by one “Modified BMW watercooled V12 gasoline engine”, rated 550hp/1500rpm. In Waffentrager’s article he said later a Kawasaki 1100hp engine were installed, but obviously that’s none sense. There was really existed a Kawasaki 1100hp engine but that is the two BMW V12 engine(Same engine on Type 5 gun tank or Type 5 medium tank) combined together for Japanese super-heavy tank O-I use. It will take much more room which Ho-Ri do not have.
Fig.17: O-I’s engine compartment arrangement. There’s no such room in Ho-Ri for this engine set.
And last here are the other questions I asked
Fig.18: Other questions I asked
I have already talked about the questions regarding C13120839500 and the engine. As for the gun with 1005m/s muzzle velocity, the Japanese never planned to make the 105mm gun achieve such a high velocity because they don’t have the enough tech back then. Also from the archive C14011075200(important fig.4) the 105mm gun was designed only to reach about 900m/s.
So, after all these, how did Waffentrager replied? I will post out the replies from my E-mail(because he deleted my replies on his blog).
Fig.19: Waffentrager’s first reply
He kept saying that my archive is not the same as his and he is using his own documents. I didn’t believe in these shit and I replied:
Fig.20: My reply
Last sentence, the Ho-Ri III he was talking about is fake. There are only Ho-Ri I(The one resembles the Ferdinand tank destroyer) and Ho-Ri II(The another one resembles the Jagdtiger tank destroyer). He even photoshoped a picture:
Fig.21: Waffentrager’s fake Ho-Ri III
Fig.22: The real Ho-Ri I and the base picture of Waffentrager’s photoshoped Ho-Ri III in Tomio Hara’s book. Many same details can be seen in Waffentrager's fake Ho-Ri III
The 4 variants of up-armoured Type 3 Chi-Nu medium tank is also fake, I will post his original article and the confirmed facts I got from Mr.Taki by E-mail.
Fig.23: 4 models of up-armoured Chi-Nu by Waffentrager
Fig.24: Mr.Taki’s reply
Waffentrager used every excuses he could get to refuse giving out the references, and finally he deleted my comments. What an asshole!
Fig.25: Our last “conversation”
Fig.26 He deleted my comment.
So, as you can see, Waffentrager is really a dick. He is cheating everybody because he think that we can’t read Japanese. Anyway I still hope he could release his reference and documents to prove me wrong. After all, I’m not here to scold or argue with somebody, but to learn new things. Also if you guys have any questions about WWII(IJA) Japanese tanks, feel free to ask me, I’m happy to help.
The O-I (オイ車 Oi-sensha) was a super-heavy tank prototype designed by the Imperial Japanese Army during the Second Sino-Japanese War after the Battles of Nomonhan in 1939. The O-I is one of the Second World War’s more secretive tank projects, with documentation regarding the tank being kept private for over 75 years at Wakajishi Shrine, Fujinomiya. Surviving files have been purchased by FineMolds Inc., and publicly previewed in mid-2015. The multi-turreted 150-ton tank was designed for use on the Manchurian plains as a supportive pillbox for the Imperial Japanese against the Soviet Union. The project was disbanded four years after the initial development began, deemed unsatisfactory for continuation in 1943 after the lack of resource material for the prototype.
History and development
After 1939, the Imperial Japanese Army quickly came to realize that previous forms of mechanized warfare were proved inefficient after their defeat at Khalkhin Gol.
Development of the super-heavy project was spearheaded by Colonel Hideo Iwakuro, the head of the Ministry of War of Japan (陸軍省 Rikugun-shō). Iwakuro opposed Japan’s advances towards the Soviet Union in 1939, and with the Japanese defeat, he decided to initiate a project to construct a heavily armored tank capable of withstanding large-caliber field cannons. Iwakuro assigned Colonel Murata of the 4th Technical Research Group to design and construct the super heavy tank in 1939. Colonel Murata noted Iwakuro’s words as described;
“I want a huge tank built which can be used as a mobile pillbox in the wide open plains of Manchuria. Top secret.”
“Make the dimensions twice that of today’s tanks.”
The 4th Technical Research Group began designing the super-heavy vehicle throughout 1940, attempting to meet Colonel Iwakuro’s vague instructions on the ultimate goal of the project. By March 1941, the research group had finished initial tank design and was ready to begin construction. The following month, a group of pre-selected engineers were chosen to partake in the building of the super-heavy tank. One recorded engineer was Shigeo Otaka, who stated they were sent to the 4th Technical Research Group’s previous headquarters in Tokyo. There, they were guided through a barracks containing multiple small fitting rooms, where they were to conduct meetings and reports on the progress of construction of the super-heavy vehicle. Towards the end of the barracks facility was a fully-enclosed room devoid of windows, with soundproofed walls to prevent external personnel from overhearing discussions related to the project. Each officer present possessed a portion of the project’s blueprint, which, when assembled, projected the full design of the tank, labeled "Mi-To". The name originated from a collection of the Mitsubishi industry and the city, Tokyo; given to the vehicle to uphold secrecy of the tank’s project.
Colonels Murata and Iwakuro
The chosen engineers voiced their concerns regarding the Mi-To’s design noting that previously, the largest-sized Japanese tank had been the prototype Type95 Heavy in 1934. Issues that had been noted with heavy tank experiments in the years preceding the Mi-To showing Japan’s generally unsuccessful testing on multi-turreted vehicles exceeding the weight of standard armored vehicles. However, with the threat of a second Russo-Japanese conflict becoming more apparent, the project continued despite the engineer’s doubts on the size and mobility of the vehicle.
Four engineers who survived to record the dealing had with the project
On April 14th 1941, the engineers began the construction of the Mi-To under secretive means. This entailed privately-made mechanical parts and equipment being shipped to the construction zone. Colonel Murata’s original concept was to complete the super-heavy tank three months after the initiation of Mi-To’s construction. This, ultimately, did not come into fruition; as technical issues on the project began to arise. Due to the limitation on material consumption by the government, the amount of parts that could be secretly shipped-in began to dwindle. By the first month of construction, essential construction resources had been depleted and the issues with the vehicle’s cooling system further caused delays. The construction of the Mi-To was postponed until January 1942, a delay of nine months.
After the Mi-To’s construction was resumed, the hull was completed on February 8th 1942. The tank had reached near-completion and was being prepared for mobility testing. Mitsubishi built the four turrets for the tank in May of the same year. Initial assembly of the tank’s armament took place soon after the turret’s superstructures were completed. However; the project once again did not have the necessary resources needed for the few remaining parts required for the final assessment. Due to this, the primary turret was removed as it lacked a 35-millimeter-thick roof plate, which had not yet arrived. Thus, the project was put on standby, until further development could continue. The total weight of the vehicle at the time was 96 tons, due to the lack of remaining structural plates and absent 75mm bolted-on armor.
O-I documents previewed by FineMolds
The date on which the construction of the tank resumed is unknown, although active testing of the tank was scheduled for late 1943. The tank was unveiled to the Imperial Japanese Army’s highest command in 1943, and received a name change to O-I. This followed Japanese naming convention (O translating to Heavy, I for First, making it "First Heavy") that was standard. In his place was Lieutenant Colonel Nakano, Murata's assistant and colleague. Tomio Hara, head of the Sagamia Army Arsenal, was also present. Following the demonstration, senior officials within the IJA requested that field trials begin in August of the same year. The tank was disassembled at 2:00 AM one night in June of 1943 and sent to the Sagami Army Arsenal in Sagamihara, 51 kilometers from Tokyo. The vehicle arrived at the depot in June, and was reassembled and tested on the 1st of August.
On the day of the trials, the O-I performed satisfactorily until the second hour of the tests. While maneuvering on off-road terrain, the tank sank into the ground by up to a meter; attempts at traversing the hull to extricate the vehicle proved fruitless, resulting in further sinking due to the vehicle’s suspension coils compressing. The tank was eventually towed out, and further testing was continued on concrete. However, the earlier damage to the suspension resulted in vehicle’s movement damaging the concrete, which in turn, further damaged the suspension bogies to the point that further testing could not continue. The trials were postponed, and later canceled the following day.
Nevertheless, the trials conducted at the testing field were considered to be a success, and the vehicle was deemed ready for use in spite of its flaws. The engineers began disassembly of the tank on the 3rd of August due to resources being limited and the inability to maintain the tank in the field. Disassembly of the tank was completed on August 8th. Two days later, the engineers noted in a log that they were to inspect the parts and conduct research to fix the issues the O-I would face.
The fate of the O-I after its field-trials which took place on the 1st of August is unclear. Russian reports claim the Japanese were in possession of a wooden O-I mock-up mounting a Daimler-Benz DB 601A engine in 1945, however other sources point to the scrapping of the remaining parts of the same year. The remains of the O-I reside at the Wakajishi Shrine, with a track link of the prototype still present.
Remaining track link of the prototype O-I tank
The O-I was conceived out of the necessity to produce an armored vehicle capable of withstanding modern weaponry being able to return fire with similar firepower. The O-I was designed to act as a mobile pillbox, supporting infantry and mechanized groups along the border of the Soviet Union. The tank had a length of 10.1 meters, width of 4.8 meters, and a height of 3.6 meters. The dimensions of the vehicle closely matched those of the Panzer VIII Maus. The tank was envisioned to have a standard thickness of 150 millimeters front and rear, in order to protect against common anti-tank weapons of the time, yet it was constructed with armor 75 millimeters thick. However, an additional armor plate could be bolted on to bring the total thickness of the armor to 150 millimeters. The use of additional armor allowed for ease of construction and transportation, while also providing the tank with additional defense. Side armor on the hull superstructure was 70 millimeters thick. The additional armor plates were 35 millimeters thick, but armor surrounding the suspension was only 35 millimeters thick. This made the tank’s theoretical armor on the side 75 millimeters. There were eight wheel-supporting beams located on both sides of the suspension area which added an additional 40 millimeters of armor to specific locations on the side of the O-I. 40 ladder pieces were placed around the tank to provide crew with the ability to climb onto of the vehicle with ease.
The two 47mm cannons used in the two frontal turrets were also modified to fit the armor layout of the tank. The weapon’s barrels were reinforced with steel to secure them to the tank, due to the standard gun not adequately fitting into the turret.
The tank was both designed and built with two inner armor plates to divide the interior into three sections; walls with two doors each and an ultimate thickness of 20mm. This allowed the crew and modules to remain relatively safe while the structure was kept safe with supporting stands. These supports allowed the interior armor plates to stay stable and also prevented collapse. Inside the O-I were two Kawasaki V-12 engines, both located in the rear, parallel lengthwise, to give room for the rear turret operator and transmission. The transmission copied that of the Type97 Chi-Ha’s, but used larger parts and gears making the total weight heavier. The vehicle had a coil spring system, with eight 2 wheeled boggies, totaling 16 individual wheels.
Sources - O-I documentation, Finemolds - O-I project report notebook 1,2,3,4,5, and 6 (Finemolds) - JP Tank Perfect Guide - 日本の戦車 原乙未生 (Hara's book) (Old sources) - 帝国陸軍陸戦兵器ガイド1872-1945 - 日本陸軍の火砲 野戦重砲 - 戦車と戦車戦 - 太平洋戦争秘録 日本・秘密兵器大全 ---------------------- Since the article Soukou and Daigensui wrote long ago is filled with inconsistencies and errors, decided to make something thats actually accurate to the reports. Wrote it on Google Docs initially, posted it to WT earlier. Will be present on Ritas blog and eventually Wikipedia.