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Imperial Japanese Navy
Kawanishi Baika
The invasion of the Japanese home islands was a genuine threat to Japanese military planners. Operation Downfall was the Allied plan to launch the final blow against Japan. This consisted of the capture of Kyushu (Operation Olympic) that would provide the jump-off point for the invasion of Honshu, near Tokyo (Operation Coronet). Given the geography of Japan, Japanese military leadership was able to narrow the likely avenues of attack. To that end, Operation Ketsugo was formulated. A critical component of the operation was special attack units and they needed aircraft in mass numbers to succeed in repelling the invasion. This provided the spark for the Kawanishi Baika.
On 2 July 1944, the Kaigun Koku Hombu issued a directive to Kawanishi Kokuki K. K. to produce a special attack aircraft. The design was to be a replacement for the Kugisho Oka Model 11 and Model 22 as well as the special attack version of the Nakajima Kitsuka. The new aircraft, called the Baika (meaning Plum Blossom), needed to be constructed from as
much non-critical war materials as possible and be of simple design to allow for production by unskilled or semi-skilled labour in small, scattered workshops. These demands were a result of the relentless Allied bombing of Japanese industry and that Allied naval forces had a stranglehold on imports of raw materials needed to sustain the Japanese military. To meet this directive, Professors Ichiro Tani and Taichiro Ogawa, both of the Aeronautical Institute of the Tokyo Imperial University, began to study a means to achieve the requirements of the task before them, supported by Kawanishi.
The engine for the Baika, the Mam Ka-10 pulsejet, was derived from the German Argus As 109-014 pulsejet, the technical plans for it having been delivered to Japan via submarine in 1944. The Aeronautical Institute of the Tokyo Imperial University studied the design and in time developed the Ka-10. A pulsejet is a simplistic engine that operates by mixing air that is taken into the engine via a shuttered or valve intake with fuel that is then ignited in the combustion chamber. The force of the explosion closes the intake and thus the
resulting gas can only be expelled through the exhaust and forward thrust is generated. This cycle, or pulse, is repeated over and over up to 45 times per second in the case of the Argus Ar 109-014.
A pulsejet has four main benefits. Firstly, due to the simple nature of the engine it can be easily built. Secondly, it can use low grade fuels. Third, pulsejets offer reduced maintenance. Finally, they have a lower cost per unit when compared to other engines. However, the pulsejet does have three major flaws – it is not fuel efficient and, due to the operating nature of the engine, it is noisy and generates significant vibration.
The choice in using the pulsejet for the Baika was clear. With the situation for Japan being what it was in late 1944 and into 1945, the Ka-10 offered a far less complex engine than a turbojet or piston engine. This meant it could be built in greater numbers by unskilled or semi-skilled labourers. Because it could use low grade gasoline it put less of a strain on the supply chain struggling to provide more refined aviation fuel. Tani and Ogawa did find that the Ka-10 suffered from having a short
service life in regard to its fuel valve. They also had concerns that the high noise of the engine would provide enough advance warning that countermeasures could be set or sent up to combat the Baika. Finally, it was realised that the vibration caused by the engine would put a strain on the aircraft, perhaps causing failures in the aircraft’s structure. The benefits, however, outweighed the disadvantages and work on the Baika design proceeded.
A meeting was called on 5 August 1945 to be held at the Aeronautical Institute of the Tokyo Imperial University. It was attended by Admiral Wata and Admiral Katahira from the Kaigun Koku Hombu, professors Naganishi, Ogawa and Kihara of the Aeronautical Institute, and Chairman Katachiro of Kawanishi. In the discussions, the Baika was selected over the rival Kugisho Oka Model 43B, the latter being seen as too complex to build in numbers quickly, especially since it used the Ne 20 turbojet. Some revisions, specifically in simplifying the design, resulted in two versions of the Baika being discussed. As the Baika was to be used to defend the home island, launch rails were to be constructed that would use a solid fuel rocket to hurl the Baika into the air. The second version incorporated a simple landing gear and it was decided that the Baika with the landing gear would be used for training pilots before they converted to the rail launched Baika. After all, given the mission of shimpfl attacks on Allied invasion ships, the pilot would not be returning and would have no need of landing gear. At the conclusion of the meeting, Kawanishi was given an order for one Baika prototype and ten two-seat trainers. The company was given a deadline of September to have the finalised design completed as well as a production plan finished. Mass production was to begin in October 1945.
Kawanishi was given the following specifications for the Baika:
– length of no more than 8.5m (27.8ft)
– height of no more than 4m (13.1 ft)
– width, with folded wings, of no more than 3.6m (11.8ft)
– speed, with the Ka-10, must be at least 463km/h (287mph) at sea level
– a ceiling of 2,000m (6,561ft)
– range of at least 130km (80 miles)
– 100kg (2201b) explosive payload
As the Baika was developed, three versions of the aircraft emerged. Two were similar except for the cockpit placement. Despite the initial direction that the Baika would be rail launched, all versions used landing gear. The first version, or Type I, had the Ka-10 pulsejet directly above and behind the cockpit – this resulted in a fairing that enveloped a portion of the front support strut for the engine. The second version, the Type II, moved the Ka-10 further back, eliminating the need for the fairing. The final version, or Type III, placed the Ka-10 below the fuselage instead of above it. With the first two, the adjustment of the pulsejet may be due to maintain the centre of gravity on the aircraft. Facilitating pilot egress was likely not the reason for the move. The need for landing gear suggests that rail launching was not the only means to get the Baika airborne. Towing or using rocket boosters may have been considered or the use of the landing gear may have simply been for training use only. It is probable that the landing gear could be jettisoned to improve aerodynamics. The Type III, with the underslung engine, would suggest that it was to be carried by a parent aircraft much in the manner of the Oka in addition to rail launching. It is unknown what the two-seat trainer version would have looked like. It is not unreasonable to assume that the warhead would have been removed and a second cockpit installed with ballast simulating the warhead, much like the Kugisho Oka Model 43 K-l Kai, the two-seat trainer for the Oka.
Initially, the Baika featured 8mm of armour protection for the pilot and although this only protected his back, it was a means to allow for some modicum of defence against interceptors firing from behind rather than ground fire. However, this was changed and the armour was removed, allowing for an increase in the warhead size up to 250kg (551 lb). While this did result in a reduction of range, it was not seen as a detriment given that the likely engagement distances would be rather less than 130km (80 miles).
On 6 August 1945, another meeting on the Baika was called. Masayama Takeuchi of the Kaigun Koku Hombu had concerns in regard to its construction and sought to have the Baika built from as little war-critical material as possible, meaning that wood would be used wherever possible. The Baika also had to have passable handling characteristics in the air to give the pilot the best opportunity to strike his target. Beginning on 8 August 1945, a team of 60 men was assembled at Kawanishi to oversee development and production of the Baika to be led by engineer Tamenobu. It all came too late for on 15 August hostilities came to a close and the Baika project came to an end before it had left the drawing board.
As a note, some sources make the case that the German Fieseler Fil03R Reichenberg, the manned version of the Fi 103 (V-l), was an influence for the Baika. There are US intelligence reports which indicate that the Japanese were well aware of the Fi 103 by October 1943 and that one was obtained in November 1944. These reports also suggest that the Japanese were very interested in the air launching techniques for the weapon. Another report indicates that the Japanese also knew of the Reichenberg project. A 1946 USAAF report shows the Baika as a copy of the Fi 103R. Finally, a manifest of cargo on the Japanese submarine 1-29 (the same that carried data on the Messerschmitt Me 163B and Me 262; see the Mitsubishi J8M SyOsui chapter for more information) listed a single Fi 103 fuselage as being onboard. The contemporary illustrations of the Baika today (including the one here) are derived from the drawings of the aircraft made by Technical Commander Eiichi Iwaya in the 1953 Japanese book Koku Cijutsu No Zenbo. Whether the Baika was truly inspired by the Fi 103R or was simply an independent design may never be known for certain.
Kawanishi Baika – data
Contemporaries
Fieseler Fi 103R Reichenberg (Germany)
Type Special Attack Aircraft
Crew One
|
Powerplant One Maru Ka-10 pulse jet; rated at 360kg (7941b) of thrust
Deployment None. Did not advance past the drawing board. |
By 1944, Japan was hard pressed to fuel her war machine with the raw materials it desperately needed. Being an island, only two means were available for Japan to receive ore, fuel and other vital materials from what holdings Japan had left. The first was by sea and the second was by air. The sea route was fraught with risk due to the US Navy and Allied submarine and warship presence in the Pacific. Thus, delivering cargo by air, while also not without risk, appeared a better option, despite the lower tonnage capacity in comparison to sea-going freighters. Therefore, the Kaigun Koku Hombu asked Kawanishi to design what would be one of only a handful of dedicated transport seaplanes of the war.
The UN knew full well the impact the US Navy’s unrestricted submarine warfare doctrine was having, which made merchant ships the primary target. By the end of the war, 1,200 Japanese merchant ships had been sent to the bottom along with five million tons of cargo. In part this was due to poor convoy methods and protection by the UN, but also because the US had broken the Japanese merchant marine cipher (the ‘mam code’). Hence, moving cargo by sea would more often than not result in the shipping being located and sunk. In 1944, shipping losses were at their highest and by 1945, while they did decline, it was because fewer ships were moving on the open ocean.
The desperation for fuel and other war materials was illustrated by the IJA’s Kokusai Ki-105 Otori (meaning Phoenix), the twin- engine version of the Kokusai Ku-7 Manazuru (Crane) transport glider. The IJA planned to use the Ki-105 as a fuel tanker which would fly from Japan to the Sumatra oil fields in Indonesia, load up with fuel and then return. However, to make the return trip the Ki-105 would consume some 80 per cent of the fuel by the time the aircraft returned to Japan. The UN looked for a better solution with a large transport capable of carrying a significant cargo load. Because a large expanse of ocean had to be crossed in order to reach what few territories the Japanese still held, the UN desired to have a seaplane to do the job. In January 1944, the IJN asked Kawanishi to develop such an aircraft.
Kawanishi was a leader in flying boat development and had gained most of its experience in designing large sea going aircraft. Two of their most successful designs were the Kawanishi H6K (codenamed Mavis by the Allies) and the H8K (Emily), with the latter arguably the best flying boat of World
War 2. The company was also not lacking in cargo flying boat design having modified the H6K to serve as a transport as the H6K2-L and H6K4-L. Even the H8K was adapted as a transport, the H8K2-L Seiku (or Clear Sky). Kawanishi had also been working on the design of the K-60, a long-range transport flying boat. With these credentials, Kawanishi was able to capitalise on their knowledge to begin the design of the HI IK Soku (Blue Sky) for the IJN.
Kawanishi was instructed by the IJN to use as much wood as possible in the construction of the Soku since a flying boat of such size would have consumed a large amount of precious alloys needed for other aircraft such as fighters. Within Kawanishi, the Soku was called the KX-8 and the initial design draft was processed rapidly. The aircraft drew heavily from the H8K being a high-wing, cantilever monoplane but overall, the Soku was much larger. The keel of the Soku was nearly identical to the H8K. To power the flying boat four Mitsubishi MK4Q Kasei 22 (Ha-32-22) radials, each developing l,850hp, were selected with two per wing. As ordered by the IJN, both the fuselage/hull and the wings were to be built of wood and under each wing would be a non-retractable float. The Soku had two decks. The lower deck could accommodate up to eighty fully equipped soldiers including a number of vehicles or a comparable amount of cargo. A smaller, upper deck housed quarters for the crew of five. The main departure from the H8K transports was that the Soku utilised a split nose that was hinged to allow the two nose sections to be opened outward to each side of the fuselage, providing ready access to the lower deck. This facilitated easier loading and unloading increasing the speed and ease of these procedures. As a measure of protection the Soku was to be fitted with three 13mm Type 2 machine guns.
Kawanishi presented the KX-8 to the IJN and the design was accepted. Authorisation was given to construct a full scale wooden mock-up of the Soku now designated the HI 1K1 for inspection before Kawanishi could proceed with the actual prototype. Construction of the mock-up commenced at the port of Komatsujima in the city of Komatsushima on the island of Shikoku (the smallest of the four main islands making up Japan). This area was selected by Kawanishi because it had access to the Seto Inland Sea which, once the prototype was built, would be needed to undertake sea and flight trials. Unfortunately for the Soku, the deteriorating
war picture saw delay after delay affect the construction of the mock-up. To add to the problem, Kawanishi was instructed by the UN in 1945 to reduce production of the H8K and instead, concentrate on building the Kawanishi N1K2-J Shiden-Kai fighter. Together, these factors would see the mock-up approaching its completion in April 1945, well over a year after the design had been initiated.
On 1 April 1945, bombing raids conducted on targets along the Seto Inland Sea saw the nearly completed Soku mock-up destroyed. With this loss, all further work on the Soku design was shelved.