Category JAPANESE SECRET PROJECTS

The Japanese purchased the He 119 V7 and V8 in 1940. See the chapter on the Kugisho R2Y Keiun for more information.

Heinkel He 162 jet fighter

See the Tachikawa Ki-162 chapter for more information concerning the Japanese acqui­sition of this fighter in April of 1945.

Heinkel He 177A-7 bomber

The UN were interested in the He 177 and negotiated to produce the bomber in Japan, with Hitachi building it under licence in Chiba in 1942. The major change was that the Japan­ese version would use four separate engines to avoid the plethora of problems the Ger­mans encountered with the original coupled engine design. Sample tools were delivered to Japan by submarine but Heinkel was unable to ship the remainder of the machining appa­ratus and jigs and production was dropped. One He 177A-7 was to be flown to Japan in 1944 to serve as a manufacturing pattern air­frame and evaluation aircraft but the bomber lacked the range, even after modification, to make the flight via the route demanded by the Japanese running through Persia and India. Some sources list the proposed plane as the Hitachi ‘He-Type’ heavy bomber.

Heinkel He 219 Uhu night fighter

The Uhu, meaning ‘owl’ in German, was per­haps the most advanced night fighter to see operational service in World War 2. The Japanese are believed to have been aware of the He 219 with full access to the relevant design data by July 1944. If this was the case, it is not known what, if anything, the Japanese did with the information.

Heinkel He 277 heavy bomber

The He 277 was, essentially, the He 177 with four separate engines instead of the coupled engines which caused so many problems for Heinkel and maintenance crews. Unlike the He 177, the He 277 would never enter pro­duction, being cancelled in July 1944 in favour of more fighters. It was believed that full details of the He 277 were provided to the Japanese in March 1944. One could assume that since the proposed Japanese version of the He 177 would use four separate engines, information on the He 277 would have been of value.

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

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.

Kurai Aerial Torpedo No.6/No.7

In April 1944, the UN initiated a design for an air dropped, anti-submarine torpedo. While not a tme guided weapon, what made the design unique was that the torpedo was winged and once in the water, entered a cir­cular pattern as it dived down. Work on the torpedo was carried out by the First Technical Arsenal Branch at Kanazawa under Com­mander Fukuba. The torpedo body was made of wood with the exception of the metal nose. The torpedo had no means of propulsion, either for flight or in the water. The wooden wings, each 1.5m (4.9ft) in length, were glued to the main torpedo body at a 20° upward angle. The wing span was approximately.9m (2.6ft) and the nose car­ried a 100kg (2201b) warhead and the total weight was 271kg (597 lb). The wood rudders were fixed at an 8° angle which, once in the water, imparted the counter-clockwise circu­lar path. The rudder was covered with a wood fairing to stop it affecting the freefall glide of the torpedo. Once the torpedo entered the water, the aluminium pin holding the fairing on sheared off and the fairing came free.

The first tests were carried out to evaluate the gliding properties of the torpedo. In all, forty drops were made of which fifteen were complete failures, the torpedo tumbling or spinning out of control. The wings were mod­ified according to the specifications given above, resulting in the Kurai No.6 which improved the gliding ability but not to a satis­factory level. Underwater testing was con­ducted by releasing the torpedo from a boat and the results showed a 17° dive angle at a speed of 5-6 knots. Colour dye released from the nose of the torpedo assisted the evalua­tors in determining how the weapon worked underwater. The maximum depth the tor­pedo could reach before the pressure over­came it was 100m (327ft). From the tests, it was determined that a form of gyrostabilisa – tion would be required.

The designated carrier plane for the Kurai was the Nakajima B6N1 and B6N2 Tenzan (known as Jill to the Allies). No modification of the plane’s torpedo rack was required. In operation, the pilot had to visually sight the target and release the torpedo from a height of 100m (327ft). An air spun vane would arm the weapon after it was released and the tor­pedo would go into a 20° downward glide. Once in the water, it would enter its circular dive with a diameter of 79m (260ft), making one revolution through a depth of 79m (260ft) after which it would continue to circle and dive until it was crushed under pressure or had struck the submarine before reaching 100m (327ft). A magnetic proximity fuse was to be used on the torpedo.

In all, 100 of the Kurai No.6 were built with many of them expended in testing. Kugisho constructed the rudders and the metal com­ponents (nose and wing braces) while the Marunimoko Company (located in Fut – sukaishi, Hiroshima Prefecture) produced the torpedo body and wings.

The poor results of the KQrai No.6 resulted in slight modifications to the design. The wing span was increased and the rudders made taller and set at 6° rather than 8°, and the nose was thickened to enhance the ability of the torpedo to penetrate a submarine hull. This new model was designated the Kurai No.7 and in January 1945, eleven test drops were made, but the weapon showed little improve­ment over the Kurai No.6. The end of the war brought the entire project to a close, the engi­neers having run out of time to solve the poor gliding performance and finalise the special fuse.

Two Kurai No.6 mock-ups were captured and shipped to the US for delivery to TAIC. What their fate was is unknown.

twin-engine ground attack aircraft

The Hs 129 was a dedicated ground attack platform which, while having problematic engines and poor manoeuvrability, pos­sessed excellent armour and the ability to carry a wide array of armaments. Allied intel­ligence reported that German sources listed two Hs 129 aircraft for delivery to Japan some­time in 1944. Since none reached Japan, it can be presumed that they were never dis­patched and the aircraft were used in Ger­man service.

Henschel Hs 130 high-altitude medium bomber

The Hs 130 was the evolution of the Hs 128, the latter a testbed for pressure cabins and high-altitude flight. Initially developed as a reconnaissance platform, the Hsl30 would later evolve into a bomber. Several prototypes were constructed and tested but the type did not enter service and was cancelled in 1944. It was believed by Allied intelligence that the Japanese obtained complete details on the Hs 130 program in July 1944. Recently pub­lished photographs showing wartime Japan­ese notes on the Hs 130, including sketches of the pressure cabin and associated systems, confirm the intelligence.

Fieseler Fi 103R Reichenberg

A US intelligence report stated that the Japan­ese were aware of the piloted versions of the Fi 103 (V-l) flying bomb and wished to use them. Codenamed ‘Reichenberg’ by the Ger­mans, 175 Fil03Rs were built but the unit

tasked with flying them, 5./KG 200 ‘Leonidas Staffel’, would not see combat. The Fi 103R I, II and III were training versions – the Reichen – berg I was a single-seater without the Argus pulsejet engine, the Reichenberg II a two – seater with no engine and the Reichenberg III a single seat version but with the engine fit­ted. In all cases, ballast simulated the war­head weight. The Reichenberg IV was the operational model. It has been suggested that the Reichenberg was the inspiration for the Kawanishi Baika.

Contemporaries

Blohm und Voss BV 222 Wiking (Germany), Blohm und Voss BV 238 (Germany), Domier Do214 (Germany), Boeing C-98/B-134 (US), Consolidated PB2Y-3R Coronado (US), Martin JRM-1 Mars (US), Martin PBM-3R Mariner (US), Sikorsky VS-44 Excalibur (US), Convair R3Y Tradewind (US), Short Sandringham (UK), Short Solent (UK)

Because the HI 1K1 was not built, the specifications given are estimates made by Kawanishi.

Type Transport Flying Boat

Crew Five

Powerplant

Four Mitsubishi MK4Q Kasei 22 (Ha-32-22) 14-cylinder, air-cooled radial engines developing l,850hp for take-off, l,680hp at 6,886ft and l,550hp at 5,500m/l 8,044ft; each engine drove a 4.3m (14.1ft) diameter, four – bladed, alternating stroke propeller

Armament

Three 13mm Type 2 machine guns with 200 rounds of ammunition per gun

Deployment

None. The HI 1K1 Soku did not advance past the mock-up stage.

There are a few Japanese wartime aircraft such as the Kugisho Tenga jet bomber that remain shrouded in mystery to this day. The Kawanishi K-200 most certainly falls into this category, a design that had it proceeded would have resulted in the first turbojet pow­ered flying boat.

Very little is known of the genesis of the K-200. Kawanishi may have been approached by the UN to initiate the project or Kawanishi may have undertaken the design themselves to see if a flying boat could be constructed using the new jet engines being designed following the success of the Ne20 turbojet. Towards the close of the war, Kawanishi was developing two other large flying boats: the Kawanishi K-60 and the Kawanishi HI IK Soku. Both of these were at the behest of the UN so it may not be unrea­sonable to assume that the UN also asked Kawanishi if they could add a jet powered fly­ing boat to the mix. Exactly when Kawanishi began to study the prospect of the K-200 is not known though 1945 is the likely year.

Depending on the source, the K-200 was either to be the replacement for all UN flying boats in service or the K-200 was to be a car­rier for a Japanese atomic weapon. The for­mer assumption would likely have depended on the performance of the K-200 had it been built. Certainly the prospect of the K-200 did not deter other flying boat projects such as the K-60 nor improvements of the H8K already in use. If the K-200 was to be such a replacement for operational flying boats and proved superior to them, it most likely would not have entered widespread service until 1946. As far as the latter, the K-200 would have needed capabilities that exceeded flying boat designs then in service in order to serve as a means to drop an atomic weapon on the US. It has been suggested that the Nakajima Fugaku was also devised to carry an atomic weapon but there is no support for this notion. The same may be said for the K-200. One can speculate as to whether the K-200 would have been any more successful in pen­etrating US coastal defences than a high flying bomber. As we shall see, the K-200 may have had a flaw that would have made any such use all but impossible.

What the definitive shape of the K-200 was to be is open to conjecture. Certainly Kawan­ishi would have utilised their successes with the H8K and to a lesser degree with the Kawanishi H6K (codenamed Mavis) as a foundation for the K-200. As such, it is likely that the hull design would have followed a similar pattern. One speculative illustration of the K-200 shows a hull not unlike the H6K but deeper, though not to the extent of the H8K. A conventional tail akin to the H8K was used but the horizontal stabilisers were mounted halfway up the vertical stabiliser. The wings appeared very similar to the H8K and were fit­ted to the hull in a like position, this being on the top of the hull and, at least for the K-200, nearly central mounted on the hull. Interest­ingly, the K-200 was illustrated with fixed wing floats, which contrasted with the retractable floats used by the H8K3 as a means to increase speed. Perhaps such a modification would have been considered for the K-200 as well.

The K-200 is shown as having an armament layout similar to the H8K1. If this was the case, a Type 99 20mm cannon was fitted in a tail turret and in the top mounted turret forward of the wings. On either side of the forward bow was a blister that would have been armed either with the Type 99 cannon or a Type 92 7.7mm machine gun. Finally, a Type 99 cannon would have been fitted in the bow. The K-200 was also probably able to carry a payload of bombs, depth charges or torpe­does.

As far as propulsion, the K-200 was to use six turbojets. They were to be mounted on top of the wings with each turbojet housed in a separate nacelle. Grouped in sets of three, the engines were fitted to each side of the hull on top of the wings. The reason for this was to minimise the amount of sea spray ingested by the engines during use. If the K-200 was of similar dimensions to the H8K, then the tur­bojet engines would have to move something in the region of 24,948kg/55,000 lb of weight when the K-200 was fully loaded. If the Ne 330 turbojet was the engine of choice, all six would produce a combined thrust of 7,800kg/l 7,196 lb. This may have been suffi­cient to give the K-200 a speed superior to the H8K2, which topped out at 467km/h (290mph).

Where the K-200 may have come up short is in terms of its range. Six turbojets would have required a significant amount of fuel in order to give the flying boat a useful opera­tional radius. As an example, the Ne 20 turbo­jet consumed around 740kg (1,6301b) of fuel per hour. The Nakajima Kitsuka, which used two Ne20 engines, carried a maximum of 1,447kg (3,1901b) of fuel (and without drop tanks only 723.5kg/l,595 lb) and therefore, at its cruise speed, could muster a 824km (512 mile) operational range. If the Ne330 con­sumed approximately 2,535kg (5,5881b) of fuel per hour at full thrust, then six would require at least 15,028kg (33,528 lb) of fuel for approximately one hour of operation at max­imum speed. Flying at a cruise speed would, of course, extend the operating range. Options to attempt to save weight may have included removing any armour, stripping the defensive armament and/or constructing the aircraft from wood as was the plan for the HI IK Soku. Even with such measures the K-200 would have been hard pressed to match, let alone exceed, the range of the H8K or more conventional piston engine flying boats.

It is not known how far Kawanishi studied the feasibility of the K-200, if at all. With resources allocated to the H8K, the HI IK Soku and the K-60 among other projects, Kawanishi designers may have put the K-200 to one side pending availability of turbojets sufficient to warrant the effort in developing the flying boat. Aside from anything else, even a reliable turbojet such as the Ne20 could only muster four to five hours of operation before it would suffer from problems. It may have been seen that preliminary perfor­mance estimates fell short of expectations and offered no significant advantage over designs currently in use or projected to enter service. Finally, a lack of materials necessary to construct the K-200 may have played a role in sidelining the design; the engine and con­struction material issue saw the K-60 ground to a halt and this may very well have extended to the K-200. Regardless of the reasons, the K-200 would never be anything more than a concept.

As a side note, following the war it was planned to construct a civilian version for use by Japan Airlines.

Kawanishi K-200 – data

Contemporaries

Beriev R-l (Russia), Martin P6M Seamaster (US)

Specifications

There is no exact information available on the Kawanishi K-200.

Deployment

None. The K-200 existed only as a concept or paper design.

As the war progressed the Japanese came to see the invasion of the home islands as a very real threat and various means of attacking the invasion fleet were investigated. One possi­bility was a bomb capable of homing in on the heat emissions of naval vessels. The plan called for the bombs to be used in night attacks when heat signatures of the ships would not be masked by the sun and other ambient heat sources. The project was undertaken by the IJA and given the name Ke – Go and work commenced in March 1944. The First Military Arsenal’s Omiya Department in Tokyo undertook development of the bolometer that would detect heat in the infrared wavelength and bench testing showed that the mechanism was workable. In fact, the sensor could detect the heat from a man’s face at 100m (328ft)! For the bomb to carry the bolometer, three different types were investigated: the B-l, B-2 and B-3. Of the three, only the first showed potential and the remainder were abandoned. A myriad of men and departments were assigned to the task of realising the B-l. Under the Military Ordnance Administration Board was Major Fujita who oversaw the gyro and airframe, Major Hizuta who also worked on the air­frame research, and Major Sonobe who addressed the amplifier. The Seventh Military Laboratory encompassed Professor Konishi of the Shikan Gakko in Osaka who handled the mathematical work, Professor Sano of the Osaka Imperial University who conducted the electrical design and Dr. Itakawa of the Aeronautics Research Laboratory who undertook the aerodynamic design studies. All wind tunnel testing was held at Rikugun Kokugijutsu Kenkyujo.

The first two bomb versions, the Ke-Go 101 and 102, were built in small numbers: ten and five respectively. The hydraulic and mechan­ical linkages for operating the bomb ailerons, coupled with the use of an electric gyro that interfered with the bolometer (A bolometer is a device used to measure the energy of inci­dent electromagnetic radiation and was invented by Samuel Pierpont Langley in 1878.), saw both of these versions aban­doned. Continued study resulted in the Ke – Go 103, 104 and 105. However, none of these designs left the drawing board although the 103 was to use an air gyro instead of an elec­trical version. The gyro only existed to ensure the bomb did not spin faster than 360° in 50 seconds. The Ke-Go 106 would be the first to be built in numbers, fifty examples in all. Overall length of the 106 was 4.7m (15.5ft) long and the wing span was 2m (6.5ft). Four main fins were fitted 1.7m (5.7ft) down the length of the bomb body with a smaller set of four fins 1,2m (3.9ft) behind the main fins, and the tail of the Ke-Go contained dive brakes. In the nose was the bolometer while the shape charged warhead was contained behind it. Two strikers that protruded out from the nose were tipped with small pro­pellers which spun and armed the bomb after release. The strikers served as the impact fuse, but a delayed fuse was also installed should the bomb strike water, in which case it would explode beneath the waterline of a ship. In short order, the Ke-Go 107 joined the program with a total of 30 bombs. The 107 had similar dimensions to the 106 version and weighed 726kg (1,6001b).

The Ke-Go was guided in flight by the bolometer. The bolometer was part of a unit that consisted of the bolometer itself, a mir­ror, motor, distributor, amplifier, relay box and battery. Heat sources passing through the bolometer would strike the mirror that, depending on where it struck, would trigger the amplifier which operated the ailerons, steering the bomb towards the heat source. The use of dive brakes slowed the plummet of the bomb, allowing time for the bomb to make adjustments in flight before impact. The ailerons could move up or down 20°. For a warhead, the Ke-Go carried between 200 to 300kg (440 to 661 lb) of shaped charge explo­sive, depending on the model. Perhaps in error, a 1946 US Navy report lists the warhead as ranging from 20 to 30kg (44 to 661b) of explosive which is very light for the size of the Ke-Go.

With enough bombs ready and available, field testing began without the bombs con­taining any payload. The test used a floating raft which measured 10m (32.8ft) by 20m (65.6ft) and was anchored in Lake Hamanako (located in Shizuoka Prefecture). On the raft wood and coal in a 4m (13ft) by 4m (13ft) pile was set alight. Both Ke-Go 106 and 107 bombs were released from altitudes varying between 1,524m (5,000ft) and 3,048m (10,000ft) but the results proved very disap­pointing. In all, around 60 drops were made but only 5-6 of the bombs displayed the zig­zag flight path that indicated the bolometer was sensing the heat from the fire and guid­ing the bomb. The remainded simply veered away from the raft. The dismal results were blamed on faulty equipment although the data collected was not sufficient to properly identify the cause of the failures. It was found that the terminal velocity of the Ke-Go 107 was 539km/h (335mph). In July 1945, further testing ceased, though work continued on improving the bomb.

The Ke-Go 108 was developed but it was with the Ke-Go 109, the last to be designed, in which the Japanese hoped the problems would be resolved and the bomb would finally prove successful. The Ke-Go 109 bomb was 5.5m (18ft long), 5m (1.6ft) in diameter, had a wingspan of 2.9m (9.4ft) and weighed 800kg (1,7641b). It was estimated that the ter­minal velocity for the Ke-Go 109 was 579km/h (360mph). It featured a larger wing span because the smaller span was considered to be one of the main causes of the poor perfor­mance of the Ke-Go 106 and 107. It was antic­ipated that the 108 and 109 bombs would be ready for test drops by September 1945. Of course, the end of the war ensured this would never happen and neither bomb was built.

Had the Ke-Go made it into service, the car­rier was to be the Ki-67 Hiryu (codenamed Peggy by the Allies). The bomb required a special brace that was fitted into the bomb bay, the apex of the brace extending a few inches past the exterior of the doors. The bomb was secured to this and the lower wing could fold to give ground clearance. On take­off, a crewman had to lower the wing and did so by means of a crank that activated a servo in the bomb, which then moved the wing. The bombardier would use bombing tables appropriate for the weight of the weapon and on release the bomb’s arming wires were pulled out along with a wire that released the dive brakes. Typically, the bomb would be dropped from 2,000m (6,562ft). After the bomb was away, the Ki-67 saw a 64km/h (40mph) increase in speed.

All of the bombs were built from wood. The only metal components consisted of the nose cap containing the bolometer and the dive brakes. In all cases, the bomb bodies were built by the Atsu Department of the Nagoya Arsenal, the gyroscope by Hitachi Co., the spring/gear parts for the timing mechanism by the Hattori Jewellery Co. and the electrical contacts for the timing mechanism by Sumit­omo Communications Branch.

Interestingly, the US would develop a simi­lar weapon, the VB-6 Felix. This was a 454kg (1,000 lb) bomb fitted with an infrared seeker in the nose that controlled the fins and guided the bomb. It was meant for night warfare, notably against ships at sea. The VB-6 was put into production in 1945 but would not see ser­vice by the close of hostilities.

Both the IJA and the UN developed spe­cialised bomb munitions during the war, some of which remained projects while oth­ers saw service. Several were dedicated to the practice of air-to-air bombing in which bombs were used to attack enemy bomber forma­tions. Although not a complete list, the follow­ing are some of the more interesting examples.

Ko-Dan

The Japanese expended some effort in devel­oping the Ко bomb. This was developed in response to observations made by one Kobayashi of high-speed photographs of det­onations of various experimental shaped charges. The basis of his theory was that the energy produced by an explosion is projected along horizontal lines with the impact sur­face. By extension, the amount of energy cre­ated is proportional to the quantity of the explosive used. To achieve a wider impact area against a target, the Ко bomb had a 2mm thick rubber nose that was mated to a 2mm thick steel case. On impact the nose of the bomb would flatten and expand, thereby enlarging the surface area and increasing the effects of the explosive pellets contained within. The Ко would be used against hard targets such as concrete emplacements. In tests, a Ко bomb with 50kg (1101b) of TNT and ultropine in an even split mixture could penetrate a lm (3.2ft) slab of concrete and utterly destroy it. It would take a regular 250kg (551 lb) bomb to accomplish the same effect. A part of this concept is known as the Misz- nay-Schardin Effect and is in practice today with modern HESH (High Explosive Squash Head) munitions and EFP (Explosively Formed Penetrator) weapons.

Mk. 7 (IJN)

Conceived around 1936 by Dai-Ichi Kaigun Koku Gijutsu-sho, the Mk. 7 chemical bomb was not given priority since at the time there was little need for such a weapon and it was thought the work needed to bring it to fruition would be too great. The idea surfaced near the end of the war, the Mk. 7 then being denied a second time in favour of guided missiles. The design was based on the 1kg (2.21b) prac­tice bomb. It had a rubber nose and within a special tail was a glass bottle of Bacillus bac­teria, most likely B. anthracis, which causes anthrax. It had no fuse or explosive charge, the impact being enough to break the bottle and release the bacteria. The planned colour for the bomb was a purple nose with a purple tail.

Mk.19 (IJN)

This was an air-to-air rocket-propelled bomb design intended for use against bomber for­mations. It weighed 7.5kg (16.5 lb). Although it was never built, the work eventually resulted in the Mk. 28 rocket bomb.

‘Silver Paper Scattering Bomb’ (IJN)

This was the Japanese version of the German Diippel, better known as ‘Window’. A 2kg (4.41b) sheet steel cylinder was packed with 200 pieces of metal coated paper measuring.3m x 8.4m (1 ft x 27.5ft). The bomb used a pull fuse that the crewman yanked to arm it and was then thrown out of the aircraft, the sub­sequent charge expelling the papers into the air to act as false radar targets. This anti-radar weapon was used heavily from 1944-1945.

In June 1941, Japan received one example of the Fi 156 for evaluation. The IJA was impressed with the ‘Stork’ and desired to have its own version. The result was the Kokusai Ki-76, codenamed Stella by the Allies. The Ki-76, despite the obvious similar­ity to the Fi 156, was not a direct copy as the prototype was completed and flying before the Japanese received their Fi 156. In com­parison testing, the Ki-76 was actually found to be superior in all areas except landing distance.

Focke-Achgelis Fa 330 Bachstelze rotorkite

This little engine-less rotorkite (the German name means ‘wagtail’) was used by a small number of German U-boats as a means to provide increased visibility to observers while the submarines were on the surface. The Fa 330, after being unpacked and assembled, was tethered to the submarine and the wind would turn the three-bladed rotor as the sub­marine moved forward. Once airborne, the observer could see up to 25 miles instead of the few miles afforded to an observer in the conning tower. One intelligence report sug­gested that the Japanese may have shown an interest in the Fa 330 had they been made aware of it.

Focke-Wulf Fwl90A-5 fighter

In 1943, the Japanese imported one example of this aircraft to pit against Japanese fighter designs and compare their performance. Figuring that Japan would use the Fw 190 in combat, the Allies assigned the codename Fred to the aircraft but none encountered.

Focke-Wulf Та 152 high-altitude fighter

In April 1945, the Japanese purchased the specifications for the Та 152 as a means to rapidly acquire a high-altitude fighter. How­ever, by this time, there was simply no way for the Japanese to act on the material obtained.

Gotha Go 242 transport glider/

Go 244 transport

In a letter dated 7 February 1944 discovered at Bad Eilsen in May 1945, the Deutsche Mitsui Bussan requested from the Germans design plans for both the Go 242 and the Go 244, the latter being a twin-engine version of the glider. No evidence has surfaced to suggest that either of these craft were sent to Japan. However, it is suggested that they were the inspiration for the Kokusai Ku-7 Manazuru (meaning ‘Crane’) glider and the powered version of the Ku-7, the Kokusai Ki-105 Otori (‘Phoenix’). Both the Ku-7 and the Ki-105 were codenamed Buzzard by the Allies.

Every aircraft creator seeks to reduce drag in their designs. The definition of drag is the force that resists movement through a fluid, which, of course, includes air. The more drag, the slower the aircraft moves through the air due to the resistance. Drag cannot be com­pletely removed from a design, but even in the early years of aviation various methods for minimising drag were investigated and many different solutions were tried. Not surpris­ingly, such applications were valued by those providing the military with aircraft and in Japan, prior to the outbreak of hostilities with the US, the Dai-Ichi Kaigun Kokti Gijutsu-sho would study such efforts in an attempt to pro­duce fast flying aircraft.

Form drag is the component caused by the shape of the body moving through the air. Therefore, when designing an aircraft the form and shape of the plane is one of the most important factors a designer has to con­sider. The wider the cross section, the more drag is produced. Having significant form drag results in lower speeds because the faster the aircraft moves through the air, the more drag force is applied to the aircraft.

Therefore, in order to realise higher air speeds, the designer must take steps to reduce drag and thereby lower the amount of drag force slowing the aircraft down.

Before World War 1 some aircraft design­ers appreciated the need to reduce drag. This often took the form of fuselages that had clean lines in an attempt to remove protru­sions and also to streamline propeller hubs to help them cut through the air more efficiently. The best example would be the 1912 Deper – dussin that won the Gordon Bennett race in Chicago, Illinois, which became the first air­plane to exceed 161 km/h (1 OOmph) (in 1913 a later model of the plane would achieve 205km/h (127mph).

At the beginning of World War 1, few of the major combat aircraft utilised significant drag reducing methods. Exhaust stacks, radiators, protruding machine guns, wire bracing, struts and engines only partially cowled predomi­nated. One of the few exceptions was the Morane-Saulnier N ‘Bullet’. Nevertheless, the rapid pace of combat aircraft development during World War 1 saw designers looking for ways to increase speed as a means to get the
edge over the enemy. The Albatross D series and the Roland ‘Walfisch’ would epitomise those efforts.

Following World War 1, the resurgence in air racing such as the Schneider Trophy in Europe and the National Air Races in America saw rapid advances in aerodynamics and drag reduction to produce fast flying racing aircraft for competition. Aircraft such as the Curtiss R2C-1 Navy Racer, the Adolphe Bernard ‘Ferbois’ (capturing the world speed record of 451 km/h (280mph) in 1924), Gloster III, Supermarine S.5, Kirkham-Williams Racer (which, unofficially, flew to a speed of 519km/h (322mph) in 1927) and the Savoia – Marchetti S.65 typified high performance race aircraft. The benefits of these innovations were not lost on military aircraft designers.

With the war clouds looming on the hori­zon, the seeds planted by the air racers of the 1920s and early 1930s were germinating in the aircraft used by the air forces of the major powers. Designs by Curtiss for the US Army Air Force were influenced by the Curtiss rac­ers while the retractable landing gear of the 1920 Dayton Wright RB racer would become

90

a hallmark of Grumman aircraft such as the F2F. In Great Britain, R. J. Mitchell would draw heavily from his experience designing Schneider Trophy racers to build the Super­marine Type 300 which would eventually evolve into the Spitfire. In Italy, Mario Castoldi, lead designer for Macci, would turn his skills in constructing racing aircraft to producing fighters for the Regia Aeronautica with types such as the Macci C.202 Folgore.

Japan, like other countries, sought to pro­duce racing aircraft and planes designed to beat world speed records. An early example was the Emi 16 Fuji-go built by Itoh Hikoki Kenyusho (Itoh Aeroplane Research Studio), which from 1920 was used in Japanese com­petitions, and the contemporary racing air­craft from Shirato Hikoki Kenkyusho. Kawanishi was not far behind with the K-2 speed racer which, despite extreme mea­sures to minimise drag, suffered from a drag – inducing radiator mounted on top of the fuselage. The K-2 achieved an unofficial speed of 258km/h (160mph) in a flight made on31 July 1921. Other refinements in aerody­namics could be seen in the Kawasaki Ki-28 of 1935 which, despite its advantages in speed, climb and acceleration, was not suc­cessful in attracting IJA contracts.

In 1938, a group of designers sought to pro­duce a high-speed aircraft to challenge the world air speed record. Once war had broken out this aircraft, called the Ken III, was soon taken over by the IJA. Redesignated the Ki-78, its development was continued under Kawasaki. During this time, it may have been the UN who decided to conduct its own stud­ies of high speed aircraft with Ktigisho assigned the task of doing so. Whether the studies were initiated in response to the IJA’s own high-speed aircraft project is unknown but the prevalent aircraft design philosophy of both the UN and the IJA prior to the war was of speed, agility and range at the expense of firepower, durability and protection.

Kugisho examined over half a dozen aspects of aerodynamics in order to produce data on what would be needed to realise an aircraft capable of significant speed. One area of research was the main wings. The shape of a wing is one of the more critical aspects of aircraft design. Factors such as wing loading, expected air speeds, angles of attack and the intended use of the aircraft all influence how the wing is shaped. For high speeds, a low aspect ratio wing is often con­sidered. Typically, these are short span wings with the benefits of higher manoeuvrability and less drag. In addition, having a backward sweep to the wing also lowers drag. The drag most associated with wings is termed induced drag, which is caused by wing tip vortices that change how the air flows over the wings. This change results in less and less lift which then requires a higher and higher angle of attack to compensate and, from this, induced drag results. Elliptical wings offer less induced drag than more conventional straight wings. However, low aspect ratio wings are more prone to larger vortices because they cannot be spread out across a longer wing. Kugisho’s study on wing shapes was the likely result of testing various airfoils in a wind tunnel to determine their effective­ness and record the results.

Another aspect Kugisho engineers reviewed were the merits and flaws of using either an inline or a radial engine and how each type reduced the form drag. In both cases the engi­neers drew up two concept aircraft and each made use of streamlining. Streamlining is the process of shaping an object, in this case, a fuselage, to increase its speed by reducing the sources of drag. One concept used the 1,159hp Daimler-Benz DB601A, a 12-cylinder, inverted-V, liquid-cooled, inline engine. This engine would be licence built for the UN as the Aichi AE1 Atsuta (the ‘A’ stood for Aichi, ‘E’ for liquid-cooled and T for first liquid – cooled engine; Atsuta was a holy shrine in Aichi Prefecture) and for the IJA as the Ha-40 before it was renamed the [Ha-60] 22. The second concept aircraft used a 1,000hp Naka – jima NK1В Sakae 11 which was a 14-cylinder, air-cooled, radial engine. This engine was a licence version of the Gnome-Rhone 14K Mis­tral Major (in engine nomenclature, the ‘N’ was for Nakajima, ‘K’ for air-cooled, T as the first air-cooled engine, while the ‘B’ was for the second version of the NK1; Sakae means prosperity in Japanese).

Kugisho would use the same basic air­frame for the engine study. It consisted of a well streamlined fuselage with the pilot mounted in a cockpit set behind the wing and just forward of the vertical stabiliser. This style was found in a number of racing aircraft such as the American GeeBee R1 and Geebee Z. Both used a standard tail-sitter configuration for the landing gear. The concept equipped with the DB 601A engine had a fuselage shape that was not unlike the Kawasaki Ki-61 Hien (meaning Swallow; codenamed Tony by the Allies) which would appear in prototype form in December 1941. The wings were mounted low on the fuselage. The fuselage appear­ance was due to the inverted-V engine which, by design, offered lower height, weight and length when compared to more conventional motors. By contrast, the concept using the NK1B had a more ovoid fuselage shape, the result of the height of the radial engine. To maintain the aerodynamic streamlining a large spinner was used. Also, in contrast to the DB 601A equipped design, the wings were mounted mid-fuselage.

Kdgisho would not produce any direct pro­totype aircraft from either concept. Instead, the results of the various studies were likely kept available as reference for engineers to access as a means of obtaining data on the aerodynamic problem. Perhaps Kugisho in hindsight considered themselves fortunate to not have expended additional expense and effort in producing working prototypes given the failure of the IJA’s Ki-78, a program that lingered on into 1944 and never met its design goals.

The DB 601A engine aircraft is shown in the colours originally used on a Mitsubishi A6M3, serial 3032, tail code V-190 of the Tainan Kokutai. It was found on Buna Airfield on 27 December 1942 in disrepair. It was a presen­tation aircraft donated by Sadahei, a civilian volunteer group. The Hukuko number was 874. The NK1В engine design is painted in the standard training orange used on prototypes and trainer aircraft.

The profile shown is based on one of the MXY6 gliders found at Atsugi in September 1945.

The paint is training orange as normally used on experimental and training aircraft.

The development of the Kyushu J7W Shinden was an ambitious undertaking. Captain Masaoki Tsuruno, the man behind the Shin­den, needed to confirm the handling charac­teristics of a canard aircraft before proceeding further with the plans and con­struction of the J7W itself. To do this, he com­missioned Kugisho to design and build three gliders that were based on his J7W1 aircraft plans. The result was the MXY6.

KQgisho drew up the design of the MXY6 with the assistance of Captain Tsuruno. Con­structed entirely of wood, the MXY6 featured a slightly swept wing, vertical stabilisers fitted inside of the wing ailerons and canards mounted along the nose of the fuselage. The braced tricycle landing gear was fixed and provided with suspension. Once the MXY6 was finalised, construction was entrusted to Chigasaki Seizo K. K. and they had completed the three gliders by the fall of 1943. Flight tri­als got under way soon thereafter and the MXY6 was found to have good handling char­acteristics which provided verification to the concept of the J7W.

For further testing, one of the three gliders was modified by having a small engine installed in the rear of the fuselage in the same pusher configuration as the proposed J7W. The engine, a Nihon Hainenki Semi 11 ([Ha-90] 11), allowed the handling under power to be studied as opposed to unpow­ered flight only. Following the conclusion of the testing of both the unpowered and pow­
ered MXY6, the validation of the canard design provided the needed proof of concept and as such the UN instructed Kyushu to pro­ceed with the J7W Shinden.

Kugisho MXY6 – data

Contemporaries

Hamburger Ha 141-0 (Germany), FGP 227 (Germany), Goppingen Go 9 (Germany), Horton Ho IIIB and Но IV (Germany), Berlin В 9 (Germany), Junkers Ju 49 (Germany), Lippisch DM-1 (Germany), DFS194 (Germany)

Type Proof of Concept Glider

Crew One

‘No longer can we hope to sink the numeri­cally superior enemy carriers through ordi­nary attack methods. I urge the use of special attack units to crash dive their aircraft and I ask to be placed in command of them.’

These words by 1JN Captain Eiichiro Jyo, commander of the carrier Chiyoda, reflected a mood he had observed in some of his pilots and men. Their feelings were that to carry on with conventional tactics was doomed to fail­ure. While death in combat was worthy, a death that did no good was shameful and would not serve the Emperor or Japan. Jyo’s words, written in a memo to Rear Admiral Soemu Obayashi and Vice Admiral Jisaburo Ozawa, would be the catalyst for the forma­tion of special attack units and from this a new weapon would arise that would become the only purpose-built special attack aircraft to see operational combat service during World War 2: the Kugisho MXY7 Oka.

Vice Admiral Takijiro Onishi is most often credited with officially forming and organis­ing the special attack units, the first of which became operational in October 1944. A piv­otal man in the formation of the UN’s Rikusentai (airborne troops), Onishi was also eccentric which did not always endear him to his superiors and so, prior to his assuming command of the UN land air forces in the Philippines, he served as a supply officer. Speaking to the officers of the 201 st Air Group, Onishi stated that because of the limited resources only a Mitsubishi A6M Reisen with a 250kg (551 lb) bomb that was crashed into enemy ships would suffice in slowing the US fleet. From this began the rise of the UN spe­cial attack force, the Shimpti Tokubetsu

Kogekitai. Their story, as well as that of the IJA’s Shimbu Tokubetsu Kogekitai, is beyond the scope of this book (however, for those interested there is a wealth of material avail­able on the subject such as David Brown’s Kamikaze and Earl Rice’s Kamikazes).

The majority of the shimpti missions were flown using types already in service. In addi­tion to the Reisen, the Kugisho D4Y Suisei (meaning ‘Comet’ but known to the Allies as Judy), Kawasaki Ki-48 {Lily), Nakajima Ki-49 Donryu (meaning ‘Storm Dragon’ but called Helen by the Allies), Aichi D3A {Val) and many others were modified, sometimes heavily, and used against the Allies, but none were specifically built from the ground up for shimpu (suicide) operations. It would be UN Ensign Mitsuo Ota, a transport pilot flying with the 405th Kokutai, who put forward a design for a piloted glide bomb.

Ota’s concept was not the only one that called for a dedicated shimpti aircraft. Other ideas were considered such as the Showa Тока (see elsewhere in this book on the Nakajima Ki-115 Tsurugi for more informa­tion), but what set Ota’s idea apart was that he wanted to have the explosive payload car­ried internally as opposed to fitting an exter­nal bomb. Also, the aircraft had to be carried and released by a parent plane and rocket boosters would be used to speed the approach and terminal dive onto the target.

Ota did not have any aeronautical engineer­ing experience and would not have been able to present a definitive plan for his aircraft. In order to help his cause, Ota sought and received assistance from the Aeronautical

Research Institute of the University of Tokyo. Professor Taichiro Ogawa headed the study of Ota’s concept while Hidemasa Kimura pro­vided the basic design of the aircraft and even produced models that were wind tunnel tested. Within weeks, the proposal for Ota’s design was drafted, the design illustrated and performance estimates presented along with the data obtained from the wind tunnel testing.

In August 1944, Ota brought his proposal to the attention of Lieutenant Commander Tadanao Miki. Miki was the department head of the aircraft design section of the Dai-Ichi Kaigun Kokh Gijutsu-sho. It is said that when Miki reviewed Ota’s concept he was taken aback and shocked at the idea of putting men into piloted bombs. However, by this time the policy of shimpu tactics had been approved and regardless of how Miki felt personally he could not deny the submission. Miki placed the design before the Naval General Staff on 5 August 1944. Air Staff Officer Minuro Genda, after looking over Ota’s plan, approved the concept and instructed chief of staff Admiral Koshiro Oikawa to set the wheels in motion for turning the design into reality. Perhaps it was ironic that the task of starting the devel­opment of the aircraft fell to Miki. Kugisho was the organisation that would develop the aircraft, which was given the initial designa­tion MXY7. Miki assembled a team of engi­neers led by three men, Masao Yamana, Tadanao Mitsugi and Rokuro Hattori, and they began drafting and refining the MXY7 design.

The MXY7 was essentially a glider bomb with a pilot providing the guidance. There were several specific factors involved in the MXY7, most of which were out of necessity. In order to conserve war materials, the MXY7 was to be constructed using wood as well as non-critical metals such as aluminium, if nec­essary. It was expected that pilots with mini­mal skill would be required to fly the machine and therefore the aircraft had to possess good handling and manoeuvrability to ensure a successful strike. Not surprisingly, instrumen­tation for the MXY7 was kept to the bare min­imum. The aircraft also had to be simple to construct so as to allow rapid mass produc­tion by semi-skilled and unskilled labour.

The MXY7’s primary mission was anti-ship. The flight profile began with the MXY7 being carried aloft by a modified Mitsubishi G4M bomber. At the point where it was within range of the target, the G4M would release the MXY7 which would then glide towards the intended victim. During the approach the pilot would ignite the rocket motors in the rear of the plane to increase its speed and close in to the target as quickly as possible. This would minimise the chances of inter­ception and present a fast moving target to defending anti-aircraft gunners.

Miki and his team completed the design of the MXY7 in weeks and by the end of Sep­tember 1944 ten MXY7 had been completed and were ready for testing. The aircraft was then renamed the Oka Model 11, Oka mean­ing ‘Cherry Blossom’. A 1,200kg (2,6461b) explosive charge was fitted into the nose and five fuses were installed, one in the nose and the remaining four on the rear plate of the charge. The fuses were armed by the pilot from inside the cockpit and they could be set to explode on impact or the detonation could be delayed by up to 1.5 seconds to allow the Oka to penetrate the target (such as a ship hull) and explode inside. The carrier for the Oka was the Mitsubishi G4M, known to the Allies as Betty. A number of G4M2a Model 24B and 24C bombers were modified by having their bomb bay doors removed to be replaced by the required shackles to hold the Oka. These modified carriers were redesignated G4M2e Model 24J. However, the Oka’s loaded weight of 2,140kg (4,7181b) far exceeded the bomber’s standard load of 1,000kg (2,205 lb) and as a consequence the G4M2e suffered from poor handling and performance.

As the Oka did not take-off on its own nor was it anticipated that it would fly at speeds under 322km/h (200mph), the wings were kept very short. For propulsion, three Type 4 Mark 1 Model 20 solid fuel rockets were installed in the tail of the fuselage. Each rocket could produce up to 267kg (588 lb) of thrust for a total of 801kg (1,7641b). The pilot could activate them as he saw fit and could fire them one by one or all three at once. Total burn time for each rocket was 8-10 seconds. Given that the Oka would have to fly through significant anti-aircraft fire as it approached its target as well as the possible aerial inter­ception by Allied fighter cover, the pilot was afforded protection through armour plate. A 19mm strip of plating was fitted along the underside of the fuselage near to the pilot’s feet while his bucket seat had between 8mm and 15mm of armour, the majority protecting his back.

As discussed above, the instrumentation was kept to a minimum. The instrument panel contained the altimeter, compass, atti­tude indicator (artificial horizon), airspeed indicator, arming handle for the fuses and the rocket motor ignition switches.

With the ten available MXY7 prototypes, flight testing was to commence in October 1944. However, the IJN did not want to wait for the results of the tests and in September, Rear Admiral Jiro Saba, director of the Kugisho Naval Aeronautical Research Labo­ratory, went to Lieutenant Commander Yokei

Oka Model 22 – data

Type Special Attacker

Crew One

Type Special Attacker

Crew One

Oka Model 43A – data (estimated)

Type Special Attacker

Crew One

Matsurra at the Munitions Ministry to sort out the arrangements for opening production of the Oka. Matsurra, who shared a similar dis­taste of the suicide concept to Miki, saw to it that much of the production was handled by military contractors to maintain secrecy and not by the private aviation industry. As such, Kugisho would build the Oka at Dai-Ichi Kai – gun Коксі Gijutsu-sho as well as at Dai-Ichi Kaigun Kokusho, and two sub-contractors, Nippon Нікбкі K. K. in Yokohama and Fuji Hikoki K. K. in Kanegawa, would provide wing and tail assemblies. It was expected that 100 Oka aircraft would be ready by November 1944.

The first unpowered flight tests of the Oka began at the Sagami Arsenal located in Sagamihara in Kanagawa Prefecture. To begin with, unmanned, unpowered flights were conducted to assess the Oka’s flight characteristics and these were followed soon afterwards by unmanned, powered flight tests. All of the Oka drops were made from the G4M2e bombers with the Okas being directed out into Sagami Bay. Flight testing was then moved to Kashimi in Saga Prefec­ture which was near the UN base in Sasebo in Nagasaki Prefecture. At Kashimi, the first manned flight of an Oka took place on 31 October 1944 with Lieutenant Kazutoshi Nagano (other sources have his last name as Nagoro) at the controls. The particular Oka that Nagano was to fly was the prototype for the Oka K-l trainer. In place of the warhead and the three rocket motors were tanks hold­ing water as ballast that simulated the com­bat weight of the Oka. Since there was no room for a conventional landing gear, a cen­tral landing skid was fitted to the underside of the fuselage and under each wing tip were rounded skids to protect the wings and pre­vent them from digging into the ground on landing. Prior to landing, the water was to be jettisoned which slowed the landing speed to 223km/h (138mph). For Nagano’s flight, a rocket booster was fitted to the underside of each wing. At 3,505m (11,500ft) Nagano was released from the G4M2e bomber and entered a good, stable glide. A few minutes into the flight, Nagano activated the booster rockets and almost immediately the Oka began to yaw. Nagano quickly jettisoned the rockets and the problem disappeared. The remainder of the flight went perfectly, Nagano bringing the Oka down without mishap after releasing the water ballast. Sub­sequent investigation showed that uneven thrust from the rockets caused the yawing and Nagano is said to have stated that the Oka handled better than a Reisen.

As flight testing and production of the Oka got underway, 721st Kokutai was formed at

Hyakurigahara Airfield on 1 October 1944 under the command of Commander Moto – haru Okamura with Lieutenant Commander Goro Nonaka and Lieutenant Commander Kunihiro Iwaki as his operations officers. The unit was nicknamed the Jinrai Butai, translat­ing as ‘Thunder God Corps’. Through October the unit received hundreds of volunteers. Those who were too old, married or were only sons, or those with significant family responsibilities, were rejected for the Jinrai Butai, leaving 600 pilots to be accepted into the unit. The 721st Kikotai consisted of the 708th Hikotai and the 711th Hikotai, each with 18 G4M2e bombers. The 306th Hikotai and the 308th Hikotai were assigned the task of escorting the Oka carrying bombers, each squadron maintaining 36 Mitsubishi A6M Reisen fighters. The unit’s initial 10 Oka air­craft were supplemented by some 40 Mit­subishi A6M5 Reisens fitted with 250kg (551 lb) bombs.

Flight testing of the Oka continued through­out November. These tests showed that when dropped from 5,944m (19,500ft) at a downward glide angle of 5.5° the Oka could achieve a range of 60km (37 miles) at a speed of 317km/h (230mph). In a nearly vertical dive it was clocked at over 966km/h (600mph). However, under combat conditions the Oka could manage 25 to 29km (15 to 18 miles). Based on the tests and flight experience, a mission profile was developed for the Oka’s deployment. Flying at a height between 6,096m and 8,230m (20,000ft and 27,000ft), the G4M2e would release the Oka when it was within 17 to 33km (10 to 20 miles) of the target. The pilot would then enter a shallow glide with an airspeed of between 371 km/h and 451 km/h (230mph and 280mph). At a point about 8 to 12km (5 to 7 miles) from the target, and from an altitude of approximately 3,505m (11,500ft), the pilot would activate the rocket boosters increasing the speed to 649km/h (403mph). Prior to striking the tar­get, he would put the Oka into a 50° dive that would take the speed up to nearly 934km/h (580mph). At the last moment, the pilot would pull up the nose to strike the ship at the waterline.

Oka pilot training was soon underway. Typ­ically, the pilot would use a Reisen to practice the Oka attack routine flying the fighter with the engine switched off. For many, they only had the opportunity to become familiar with the Oka while it sat on the ground. A few were fortunate to make an unpowered flight using one of the MXY7 trainer prototypes. As expected, accidents occurred and on 13 November 1944, the Oka claimed its first casualty. Lieutenant Tsutomu Kariya exe­cuted a perfect drop from 2,987m (9,800ft)

and was bringing the Oka down for a landing. He inadvertently released the water ballast from the nose tank, leaving the rear tank full. This immediately caused the nose to pitch up, putting the Oka into a stall that Kariya was unable to recover from, the plane crashing into the ground. Kariya was pulled from the wreckage but within a few hours had died from his injuries.

By December 1944, Kugisho had produced 151 Okas and the Dai-Ichi Kaigun Kokusho production was also well under way. Attempts were made to deploy the Oka to units outside of the Japanese home islands. Fifty were dispatched to the Philippines aboard the carrier Shinano, but on 29 Novem­ber 1944 the ship was sunk en route. Only a handful would reach other bases, notably in Okinawa and Singapore, and none would see combat. Even though the 721st had yet to see combat, there were some who realised that the G4M2e bomber would be easy targets for enemy Fighters and the odds of actually reaching the target were small. Conse­quently, morale dropped as the Oka was seen as a waste of a pilot who could be used to bet­ter effect elsewhere. The vulnerability of the G4M2e was vividly displayed when the 721 st went into battle for the first time on 21 March

1945. Attacking US Task Group 58.1, all 18 bombers (of which 15 were Oka carriers) were shot out of the sky by US Navy fighters along with their fighter escort before they could get within attack range. Again, the story of this and subsequent Oka missions are beyond the scope of this book but the inter­ested reader can find many excellent sources of information on the topic.

Following the Oka’s disastrous debut, reviews of gun camera footage from the US Navy fighters and from pilot debriefings revealed the existence of the new weapon for the first time to the Allies. At first it was thought that the Oka was simply a large, anti­ship bomb. This would change when four to six examples were captured near Kadena Air­field after the Allied victory at Okinawa. Only then was the aircraft’s true nature made known to Allied intelligence. The Oka was subsequently given the codename Baka by the Allies, the word baka meaning ‘fool’ in Japanese.

Production of the Oka Model 11 ceased in March 1945 with the Dai-Ichi Kaigun Koku Gijutsu-sho having built 155 and the Dai-Ichi Kaigun Kokusho constructed a total of 600. One Oka Model 11 was fitted with sheet steel wings made by Nakajima but no other exam­ples were produced with this feature. To help improve the training regimen, once the Dai – Ichi Kaigun Koku Gijutsu-sho had completed their run Oka production was switched to the Oka MXY7 K-l trainer. In all, 45 of the K-l would be completed and placed into the pilot training program.

Clearly, the G4M2e carrier aircraft was too slow and easy prey for defending Allied fighter protection. In addition, the short range of the Oka Model 11 compounded the prob­lem. Consequently, KQgisho decided to utilise the superior Kugisho P1Y Ginga (Allied code – name Frances) as the carrier aircraft and also to give the Oka a longer range. This adapta­tion was called the Oka Model 22.

The primary change in the Oka Model 22 was the use of the Tsu-11 thermojet engine in

Oka Model 22 in the colours of the example found at the close of the war and now on display at the Smithsonian Air and Space Museum.

place of the rocket boosters. This consisted of a lOOhp Hitachi Hatsukaze [Ha-11-11] 11 4- cylinder, inverted inline engine driving a sin­gle-stage compressor. Fuel was injected into the compressed air that was then ignited, pro­ducing up to 200kg (440 lb) of thrust. To com­pensate for the weight of the engine and fuel, the warhead had to be reduced to 600kg (1,323 lb). Finally, as the P1Y was smaller than the G4M2e, it was necessary to reduce the wing span by lm (3.2ft), although the length of the Oka Model 22 was increased by.8m (2.6ft). These changes improved its range of up to 129km (80 miles), although 65km (40 miles) or less was considered achievable under combat conditions. A rocket booster could be fitted to the underside of the fuse­lage to increase speed during the terminal dive.

Once the design of the Oka Model 22 was finalised, Kugisho began a production run of 50 aircraft even before flight testing was underway. Aichi Kokuki K. K. was contracted to construct a further 200 Model 22 aircraft, but due to US B-29 bomber raids Aichi’s pro­duction lines would never enter operation. Once the first handful of Oka Model 22 aircraft had been made available their testing began. Thanks to its short wings, a high stall speed of 334km/h (207mph) and high landing speed made a soft landing impossible. Test pilots were instructed to abandon the Oka rather than make a landing. Lieutenant Kazutoshi Nagano took the Oka Model 22 up for the first time on 26 June 1945. The flight would also be his last. After being released from a modified Kugisho P1Y1 at 3,658m (12,000ft), the Oka went out of control (another source states that the wing rocket boosters fired acciden­tally, causing the Oka to crash into the Ginga, damaging the Oka’s controls). With no ability to regain level flight from the plummeting Oka, Nagano was able to extract himself from the stricken aircraft but his parachute only partially opened before he hit the ground and was killed. A second test model was ready in August 1945 but the war ended before it could fly. Although fifty Oka Model 22s were built, the carrier, the Kugisho PI Y3 Model 33, would never leave the drawing board. The com­pleted Oka Model 22 were retained in Japan for use against the expected Allied invasion force.

Kugisho continued to investigate ways to improve the performance of the Oka and a series of models were planned around the Ktigishb Ne 20 turbojet. The first was the Oka Model 33 which was simply the Oka Model 22 enlarged to accept the Ne20 (or as one source states using the Nel2B jet engines that had been built prior to the shift to the Ne20 development). For a carrier, Kugisho planned on using the Nakajima G8M1 Renzan (known as Rita to the Allies) but with the fail­ure of the Renzan to enter production, the Oka Model 33 was quickly shelved without any prototype being constructed. This was followed by the Oka Model 43A. Larger in dimensions in comparison to the Oka Model 22, the Oka Model 43A was designed to be launched from submarines such as the Sen Toku class. To facilitate storage on such boats the wings were foldable, but with the Allies in complete control of the seas the Oka Model 43A was soon put aside and work begun on the Oka Model 43B instead.

This version was designed to operate from caves and launched by a catapult. It retained the folding wings to allow the production lines to be set up in cramped, underground sites or caves as well. Unlike the previous models, the Oka Model 43B was all metal, used a central skid and in order to better facil­itate target penetration the pilot could jettison the wing tips. Like the Oka Model 22, a rocket booster could be carried under the fuselage. A full scale wooden mock-up was completed in June 1945 and was promptly approved for production. Aichi were tasked with construc­tion of the Oka Model 43B at their Gifu and Oyaki factories but the war ended before the first prototype was completed. However, a catapult ramp was built at Takeyama, near Yokohama, and pilots destined for the Oka Model 43B were being given instructions on catapult launching as they waited for their air­craft to be delivered.

A hybrid Oka was considered which was called the Oka Model 21. The Tsu-11 engine was to be removed from the Oka Model 22 to be replaced by the standard rocket booster system as used on the Oka Model 11. This may have been contemplated as production of the Tsu-11 engine was slow and was not keeping pace with the Oka Model 22. The proposal, however, never proceeded past a single prototype.

Whereas all previous Okas, with the excep­tion of the Models 43A and 43B, required modified bombers to carry them aloft and launch, the Ne20 turbojet equipped Oka Model 53 was designed to be towed into the air. As such any aircraft, with the addition of a tow line and having enough power, could be used to tow the Oka Model 53 into the air. Nothing came of this design due to the end of the war. However, it is worth noting that some contemporary illustrations show the Oka Model 53 without a cockpit, which would turn the type into a glider bomb. For guidance, it is speculated that upon release from the tow aircraft, it was either radio controlled from a parent plane or used infrared or acoustic homing to guide itself to the target. This con-

cept has not been verified in wartime Japan­ese sources and could be post-war conjec­ture.

A derivative of the MXY7 K-l was planned and this was known as the Oka Model 43 K-l Kai Wakazakura (meaning ‘Young Cherry’ in Japanese). This was to be the definitive trainer for pilots destined for operational Oka models. A second cockpit was installed in the nose in place of the warhead, flaps were fit­ted to the wings to help with landing and, like the K-l, the Model 43 had a central landing skid with wing bumpers. It also included a single Type 4 Mark 1 Model 20 rocket in the tail to allow the student to get a taste of powered flight. By the close of the war only two of the Wakazakura trainers had been completed.

Perhaps one of the more unusual uses for the Oka occurred in Singapore. The handful of Oka Model 11 aircraft that were received by units in Singapore were, for the most part, grounded because they did not not have their

G4M2e parent aircraft. In order to get some use from the Okas, mechanics planned to fit them with floats cannibalised from unser­viceable or available floatplanes such as the Aichi El ЗА (known as Jake to the Allies). It is not known exactly how the floats were to be installed but crude fittings could have been fabricated to attach a float under each wing. It is believed that the float equipped Okas were to be positioned along the Straits of Johor that separate Johor from Singapore and be used in conjunction with Shinyo special attack boats. Another unknown is how they would have performed given the short burn time of the rocket boosters let alone handling qualities across water. It can be surmised that performance would have been very poor. By comparison, the German Tornado attack boat used two floats from a Junkers Ju 52/3mg5e and was powered by an Argus 109-014 pulse-jet. Trials would prove a failure as the boat could not operate on anything but calm seas without capsising.

Developed and produced from 1941 to 1942, the To-З was a cluster munition and initially designed to combat aerial targets. However, the To-З turned out to be more effective against ground targets. Thirty to forty To-3 bomblets could be carried in a dispensing container or modified underwing bomb racks could carry several of the To-З bomblets. Once released, either from the container or the rack, the To-3’s vane would spin, arming the munition. Use of the To-З was performed on a limited basis and production ended in

1942.

Та (IJA)

Evolving from the To-З was the Та. Each Та bomb was a 40mm hollow charge weighing.33kg (.741b). It used fixed tail fins. When attacking airborne targets, canisters contain­ing between 30 and 76 of the Та bombs would be released. A burst fuse would open the can­isters, usually just after release, to scatter the Та bombs. The loaded canisters weighed 30kg (66 lb) and 50kg (110 lb) respectively and the Та was first used operationally in 1943 with Japanese pilots claiming a number of kills using the weapon. Typically, the Та was far more effective when used against more densely packed bomber formations.

Та-105 (IJA)

The Та-105 came from the need to attack Allied shipping during the expected invasion of Japan. The Ta-105 was the Та bomblet enlarged to carry a more substantial payload. The bomblet had a 100mm hollow charge that was capable of penetrating up to 140mm of armour plate. Unlike the Та, the Ta-105 used folding tail fins that deployed upon release. Each canister contained 21 Ta-105 bomblets.

Though the Japanese had no interest in the ‘Tante Ju’, the Allies thought the Japanese would be using the transport in action. This idea may have stemmed from a May 1939 flight made by a Ju 52/3m to Japan to bolster trade relations. As such, the plane was code­named Trixie.

Junkers Ju 87A ‘Stuka’ dive bomber

In 1940, a single Ju87A was sent to Japan for evaluation. By 1939, all A models had been withdrawn from frontline German service, and after flight testing and study the plane was put into the collection of the Tokorozawa museum. However, it was lost when the museum was bombed. The Allies, believing the Japanese would be using the Ju87, assigned it the codename Irene.

Junkers Ju 88A-4 bomber

The Japanese acquired a single example of the Ju88A-4 in 1940 for the purposes of test­ing and evaluating the aircraft as well as for the study of the design. The Japanese had no intentions of producing the bomber but nev­ertheless the Allies thought it likely they would and thus gave the Ju 88 the codename Janice. As an aside, one intelligence report states that the Mitsubishi office in Berlin had a number of ‘Ju 88K-5’ (the export version of the Ju88A-4) aircraft and parts shipped to Japan, perhaps in 1943, though this has never
been verified and only the single Ju 88A-4 is known to have been delivered.

Junkers Ju 290 long range heavy bomber

The Ju 290 was initially a heavy, four engine transport aircraft that was reworked into a long range maritime reconnaissance and bomber aircraft. It was felt that by October 1943, the Japanese were in possession of the complete details of the Ju 290. Even if this was the case, it would appear the Japanese did not act on the information and they may have been more interested in the Ju 390. There is no evidence to suggest that the Ju 290A-7 was ever adapted as a ‘nuclear’ bomber for the Japanese, especially in light of the fact few A-7 models were ever completed. Some sources suggest that Ju 290 flights were made into Manchuria carrying documents and other intelligence, possibly in exchange for raw materials from Japan, but information has never surfaced confirming these flights and popular opinion in the face of current evi­dence is that they did not occur.

Junkers Ju390A-l reconnaissance bomber

In 1944, the IJA was very interested in the potential of the Ju390 as a strategic bomber and sought to obtain the rights to the aircraft. In the fall of 1944, the Japanese acquired the manufacturing licence and design plans for the Ju390A-l long-range bomber reconnais­sance aircraft. By 28 February 1945, Major – General Otani of the IJA was to have collected the plans and licence from the Germans but it is unknown if this ever occurred. In any case, the Ju 390 V3, which was to be the pro­totype for the bomber reconnaissance design, was never built.