Type 4 Medium Tank, 'Chi-To': The Last Tank of the Japanese Army

9/5/21

Alright: after far too long, I’ve finally gotten around to writing an article on a Japanese tank. Although my interest, and so my amount of source material, is greatly centered around aircraft, this tank is one I have been passively collecting material on for a while. So, the Chi-To is probably the only (experimental) Japanese tank that I feel I can comfortably cover fairly comprehensively.

This article will encompass the whole history of the Chi-To medium tank to the best of my ability, and also describe the general policy shift of Japanese armored vehicle development which directly affected its course. Due to the amount of information, this has become much longer than I originally anticipated (over 10,000 words...). Hardly a digestible article at this point, this page at least serves as a collection of information.

Please note that the information available for this vehicle is incomplete, and there are various theories that are still under research by many people, things may be subject to change. In this article, I am mainly operating on the theory that only one vehicle was ultimately completed. Based on the verifiable data I have encountered, this seems the most likely. However, there is also considerable (but, mostly anecdotal) evidence that multiple examples may have been in operation, which will be explained.

If corrections are found to be necessary, they will be noted below.

Japan's First Jet Plane [3/3]: The Fate of 'Kikka Kai' & Variant Development

 [Part 1] [Part 2]

Pilot Susumu Takaoka

  On the afternoon of August 7th, 1945, Lieutenant Commander Susumu Takaoka boarded the cockpit of the Kikka Kai at Kisarazu AF. The summer weather was clear, and a southward 7 m/s sea breeze was received from one end of the 1,800 m runway. The sky was a pure blue, and he squinted his eyes at the brightness of the clouds. 

Assigned to the development of what became the 'Kikka Kai' since the fall of 1944, Takaoka was present for all stages of development including the planning, wooden mockup examination, completion exam and aerial testing of the all-important Ne-20 turbojet below the belly of a Type 1 Attacker. 

It had a triangular fuselage cross-section similar in appearance to musubi rice, an airframe smaller than the Reisen, and lowly positioned engines. Looking at the actual plane during the completion examination, I wondered if it could fly. I felt that if it could fly, it would be fast, but somehow the wings seemed weak, among other things...

Before the first flight, several considerable issues had been identified which required caution. 

• There was a considerable delay to the effectiveness of the throttle on the engine.
• The engine could spontaneously seize if the throttle was reduced to 6,000rpm or below.
• Due to the light loading, the flight would be with minimal fuel and a second landing pass may not be possible.
• The braking of the landing gear was highly inadequate.

Despite these concerns, the first flight was to continue as it were. The breakneck development pace of the Kikka permitted no delays in anticipation of mass production and deployment. It was necessary to acquire crucial flight data as soon as possible.

Japan's First Jet Plane [2/3]: Until the Completion of 'Kikka Kai'

[Part 1]

1945: B-29s drop incendiaries on Yokohama.

  As the year changed into 1945, the state of the war in Japan became increasingly tragic. US strategic bombings increased heavily, and B-29s trailing across the sky, mainly from the Saipan air base, became a daily occurrence. While cities were decimated by mass-bombing, goods and resources dwindled, and the production ability vital to the existence of the war effort was chiseled away. The reality of the situation became painfully clear to the public. The Army and Navy struggled to continue fighting at the end of the rope.

As described in the previous article, the 'Mk. 2 Weapon' became formalized as the special attacker 'Kikka' at the end of 1944, and on the 4th of the following January, the contents of the Navy's request draft were confirmed. In response to this plan request, Nakajima submitted projected performance calculations for the 'Kikka' which can be viewed here.

However, the development of the powerplant for Kikka - that is, the 'Ne-12' turbojet (*name changed from 'TR12' around this time), was extremely slow. Although it was being prepared for further prototyping as the lightened and improved version 'Ne-12B' at the start of this year, these indigenous Japanese turbojets were already recognized by this time as fundamentally flawed.

In fact, due to the incessant plague of technical problems, and the recognition of the 'BMW 003A' diagram that had been received during the last July, Tokiyasu Tanegashima, the lead of jet engine development in the Navy, had expressed at the end of December 1944 that the indigenous turbojet engines should be abandoned. Work was instead to be consolidated on a Japanese model engine based on the format of the successful German BMW 003A.

Fake Japanese Super-heavies

In 1939, the Imperial Japanese Army suffered total strategic defeat at the hands of the Soviet Union surrounding the village of Nomonhan, in Manchoukuo. This had been Japan’s first significant deployment of armour against a modern army. Tank development in Imperial Japan was still in its initial stages by the time the border conflict at Nomonhan began.

Japan had constructed a series of fortifications in Manchuria and Central China under the supervision of the Continental Fortification Research Committee, a department under the Imperial Army. This committee oversaw all major defenses in the region against the Soviet Union and Chinese warlords. Shortly after the Nomonhan Incident, the committee submitted an idea to construct special purpose tanks that were capable of breaking through heavily defended Soviet lines and force the Soviet armies back out of taken Manchurian lands. 

Historical Background

Colonel Hideo Iwakuro, an officer in the Military Affairs Bureau Tank Research Team, took an interest in the concept of a super-heavy tank capable of pushing through Soviet defensive lines, unmatched in firepower and armour. Japan built and tested an array of multi turreted heavy tanks from 1925 to 1938 in an attempt to implement a breakthrough vehicle. However, these tanks all had the same underlying issues: their armour was too thin to protect against anti-tank guns, and their armaments were inadequate. Due to weak engines, these prototypes lacked sufficient speed and mobility. But due to the large size of these engines, they forced the chassis to be larger. 

In the early months of 1940, Colonel Iwakuro along with a team of twenty engineers from the 4th Technical Research Group designed the superheavy tank at their headquarters in the Tokyo area. The superheavy tank project proceeded under the temporary name Mi-To (later, O-I). Construction work would be performed by the Sagami Army Arsenal in secret. As was customary with Japanese heavy tanks, the Mi-To had a multi turreted layout with two auxiliary turrets in the front part of the chassis, one primary turret in the center of the hull, and a machine gun turret located at the rear of the chassis. The tank design was heavier and larger than any other tank of its time. Basic in its shape, the vehicle kept a box-like appearance for ease of manufacturing and assembly of its plating.

Technical drawing document of the O-I super-heavy tank. One of various drawings purchased by Finemolds in 2014. (Source: author's collection)

Japan's First Jet Plane [1/3]: The Unofficial Development of 'Kikka'

  From June 19-20, 1944, a large scale air attack against the US Navy task force covering the invasion of Saipan Island ended in a devastating defeat for the Japanese Navy.

The 1st Mobile Fleet, the main carrier aviation force of the Japanese Navy, failed to effectively cooperate with the exhausted land-based 1st Air Fleet which was supposed to offset the US numerical superiority. As a result, the 1st Mobile Fleet launched the attack alone, and was annihilated by the US Task Force 58 which outnumbered it nearly two to one in an event appropriately dubbed by US aviators as the "Great Marianas Turkey Shoot".

This 'decisive battle' Operation Mk. A (ア号作戦) ended quite decisively in favor of the American forces, with the loss of the Japanese fleet carriers 'Taihou', 'Shoukaku', and 'Hiyou' along with the grand majority of Japan's carrier aircraft groups, crippling the Japanese Navy's carrier aviation force beyond repair. The subsequent fall of the Marianas triggered the collapse of Tojo's Cabinet and placed the mainland of Japan within the range of large-scale B-29 strategic bombings for the first time.

However, despite the heavy blow, land-based units of the Navy's Air Service still remained, and the Army's Air Service had not been subject to the annihilation at the Mariana Islands. Moreover, Japan's 'life-line', the southern resource transfer route, was still intact. Though ultimately set for a total defeat, Japan still possessed the ability to continue the war for the time being, and to this end, the characteristically Japanese plan for a 'decisive battle' against the US Navy was borne once again.

It was plainly clear to the Japanese military that the location of this air battle would be at the Philippines, where the US forces would undoubtedly move in to sever the aforementioned southern resource transfer route, by estimation, about 6 months after the fall of the Marianas Islands. The Army and Navy launched joint research into the preparation of forces for this event in August of 1944. This newly planned 'decisive air battle' was thought to be the last time the Japanese military could be capable of dealing a critical blow to the US Navy.

Ki-201 ‘Karyū’: The Me 262 Domestic Production Plan

Me 262 A-1a

  At the dawn of 1944, the German jet fighter Messerschmitt 'Me 262' was nearing the beginning of its service life. Due to issues with its power-plant and interference from the high command, the aircraft had been in the testing stage since 1941. In the coming months it would finally enter mass production. This aircraft achieved revolutionary performance; exhibiting a top speed of 870km/h, a cruising distance of 1,050km, and a climb rate of 1,200m/min. The bomber-devastating armament consisted of a quartet of 30 mm machine cannons and 24 rockets. On paper, it was the world’s best interceptor at the time.

Ne-0 ramjet on a Type99 Light Bomber - IJA's first jet engine.

It is comparatively little known that Japan had indigenous jet engine programs prior to being influenced by German technology. The development of original Japanese jet engines began in 1941-1942, but they wouldn’t materialize as prototypes until 1943. In the typical fashion of the Japanese military, the Navy and Army did not collaborate on this ordeal. As such, duplicate research efforts were conducted simultaneously.

The testing of indigenous jet engines were plagued with troubles ー to be brief; major issues such as total failure of the engine itself during operation, to performance problems like low thrust output and high fuel consumption rate, were unavoidable. By 1944, the most advanced Japanese turbojet developments from both sides only provided about 300kg of thrust. At this point the Japanese were several years behind their German counterparts. However, with limited assistance, an impressive technological leap was soon to be achieved.

O-I Superheavy Tank: A Complete History

The Battle of Khalkhin Gol had been a devastating defeat for the Empire of Japan in 1939. The Kwantung Army suffered total strategic defeat at the hands of the Soviet Union surrounding the village of Nomonhon. This had been Japan’s first significant deployment of armour against a modern army. Tank development in Imperial Japan was still in its nascent stages by the time the border conflict at Nomonhon began.

Notebooks belonging to the engineers working on the O-I/Mi-To tank project, and
where majority of the source material from this write-up derived from, including all drawings.