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.