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

Me 262 A-1a

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

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

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

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

Japanese Interest in the Me 262

It was in the early months of 1944 that the Luftwaffe High Command revealed the existence of their secret jet and rocket-propelled fighters to Japanese representatives in Berlin for the first time. In previous years the Germans had been reluctant to disclose their experimental weaponry to the Japanese, but as development progressed and the war situation worsened, they opened up more or less entirely. The Japanese did not waste any time to request more information, and in March, Hitler and Göring agreed to release such material to Japan. Three requests were subsequently made on April 1st:

1. Send Messerschmitt jet technicians to Japan
2. Permit the training of Japanese technicians in Germany
3. Allow the purchase of rights for the licensed manufacture of the Me 163 B and Me 262 A-1. 

Japanese submarine I-29 "Matsu" (Pine Tree)

In addition, by the beginning of that month, basic survey sketches and illustrations of the Me 163 B, Me 262 A, and various German jet & rocket engines were already turned over to Japanese attaches within Germany. Submarines Ro-501 and I-29 departed weeks later en route to Japan with these limited materials distributed among their cargo. Neither of these submarines would actually arrive in Japan, both being intercepted and sunk en-route. Only a very small amount of technical data survived with Commander Eīchi Iwaya, who would later depart I-29 during its stop at Singapore and arrive in Japan during mid-July of the same year.

The Germans agreed to release the manufacturing rights for the Me 262 to Japan in May, but the negotiations did not conclude this early, and the plans weren’t to be made available to the Japanese until the autumn of that year. During the interim Japanese representatives visited production facilities for the Me 262. They were instructed of the manufacturing techniques by August Bringewald, an overseer of Me 262 production in Germany. It was clear that Japan could not mass produce Me 262 without modifying the production techniques accordingly to their own, and would require German specialists to supervise the manufacturing process accordingly. Finally, in July, orders were issued to Messerschmitt to begin preparing the blueprints and materials for the manufacture of secret aircraft and engines to be delivered to the Japanese. On the 23rd of the same month, Göring approved the delivery of one Me 163 B and one Me 262 A to Japan, but this decision was upended by Hitler in August.

The unassuming BMW 003 drawing which revolutionized Japan’s jet program.

Around this time in Japan, the limited technical information pages to survive with Commander Iwaya from I-29 were received, as previously mentioned. Among this of relevance was an Me 262 operations manual, and a single cutaway of the BMW 003 turbojet. Despite only being a copy of a cutaway reduced to 10x15cm, this drawing was studied extensively and garnered a massive interest, because in Germany the BMW 003 was already in practical use. For small parts that were not clear on the drawing, even so little as individual lines, educated guesses were made. Using what could be learned from the layout of this drawing, the Japanese paused and re-examined their entire jet program.

In necessity of efficient development given the war situation, it was decided to unite jet development cooperatively between the Army and Navy, a practice that scarcely occurred in earlier years. The Army’s turbojet projects were completely canceled, while the Navy’s turbojet developments were to be furthered by implementing axial compressor stages learned from the BMW. Addition, a tri-company project was begun to procure high-thrust class axial turbojets, reverse engineered from the diagram of BMW 003. These engines were the following:

1. Ishikawajima Shibaura Turbine’s Ne-130: 908kgf thrust.
2. Nakajima Aircraft & Hitachi Aircraft’s Ne-230: 885kgf thrust.
3. Mitsubishi Heavy Industries & Japan Steelworks' Ne-330: 1320kgf thrust.

The History of the Me 262 Domestic Production Plan

Basic outline of Japanese turbojets.

Concurrently with the planning of these aforementioned engines, an airframe to mount them was devised. The summary of a 'Rocket Plane' assigned to Kawasaki Aircraft was included in the Army's September 1944 aircraft prototype plan. In the general outline, it was labeled as the ‘Me 262’, and the engine model was listed as the TR230 or TR330. Within the engine prototype plan issued in the same month, the engines noted as “for Me 262” were the TR140 and TR330, but curiously not the TR230.

[TR140 later became the Ne-130, and TR230 and TR330 are early names of Ne-230 and Ne-330 respectively.]

From these extant materials, it has been deduced that Me 262 was initially assigned to be designed and produced domestically by Kawasaki, and would mount the most successful of the three new turbojet models in development. According the prototype plan, the order of development should be issued during October 1944, the first prototype should be completed in December 1945, and the practical examination should concluded by June 1946. No prototype 'Ki' number was assigned to this plane, so the plan was clearly very preliminary. Unsurprisingly, the development order was not issued at the scheduled time, possibly a result of the ongoing negotiations with Germany. Complete technical and manufacturing plans for the Me 262 were delivered to the head of the Messerschmitt foreign export branch, a certain Dr. Thun, in October. Later that month Japanese representatives advised the Germans that only the Army was planning to put the Me 262 into mass production. Two mass production plans seem to have been requested, one for 100 aircraft a month, and another for 500. By December, all the necessary contracts regarding the Me 262’s licensing had been signed and concluded.

Chief Designer of 'Karyuu'
Engineer Iwao Shibuya

Although Kawasaki had been originally selected as the Me 262's development company, at some point between October and December of 1944, it is evident that the plan was transferred to Nakajima. The reason for this is not recorded, though it was possibly due to Nakajima’s position close to the development and construction of jet engines, with the Ne-230 under development. Kawasaki had also experienced an increased assignment of work at this time, which may have rendered the company unable to viably develop such a national first as a high-performance jet plane. A plan name for the aircraft was now established — it was the 'Ki-201' with the unconventional designation “Karyū” — the Fire Dragon, and development was ordered by the Japanese Army Air Headquarters. The project would be held cooperatively between the Army and Navy, with the Army in charge of the development of the airframe, and the Navy the engines. The design team was assembled at Nakajima under Iwao Shibuya and began basic research on the Ki-201 design in January 1945.

The principle outline of the aircraft required was a twin-jet fighter-attacker capable of engaging enemy jet fighters, rocket planes, and high-altitude bombers. The performance requirements were a maximum speed of 800km/h or more, a practical ceiling of 12,000m or more, and a cruising range of 800 – 1,000km or more. According to the 'Rocket-Weaponry Military Strength Improvement Plan' drafted in December, where the plane is first known to have been mentioned, prototype #1 was rescheduled to be completed in July 1945, 5 months earlier than the original planned date of the "Kawasaki Rocket Plane", with two more aircraft in August, followed by three more in September. It was also desired to increase production beyond this, and service 20 aircraft in August as well as September. Around 100 aircraft were generally expected to be serviced throughout 1945 when production plans were achieved, with two to three squadrons (112-168 planes) active by March 1946.

The crew of U-864 before their final mission to the Far East.

Unfortunately for these expectations, Germany’s final attempts at technological assistance did not proceed smoothly. On February 9, 1945, the German submarine U-864 was sunk four kilometers west of Fedje, Norway by the British HMS Venturer. It had experienced a large number of setbacks, delaying its intended embark to Japan. On board were the parts and plans for manufacturing the Me 262 A, Me 163 B, BMW 003, Jumo 004, and HWK 509. Also lost in the interception were two instrumental Messerschmitt engineers, Riclef Schomerus and Rolf von Chlingensperg, who were intended to assist with the development of jet aircraft and direct the manufacture of Me 163 & Me 262 in Japan, respectively. The Japanese were now left almost entirely in the dark — the only substantial data on German jet technology within their possession was still the very few pages departed from I-29 the previous year.

The 6 Month Design Period of ‘Karyū’

Due to the situation the development schedule was delayed, the planned completion of the basic design was now set for June 1945, the first prototype was reverted to the original schedule of December 1945, and the first 18 production aircraft were to be delivered by March 1946. Even in the absence of German manufacturing prints, the team at Nakajima began the basic design process of Ki-201 in April 1945. The last German mission to Japan, submarine U-234, departed on the 15th of the same month. Among its expansive cargo were the actual airframes Me 262 A, Me 163 B, and evidently Me 309, divided into many crates and complete with manufacturing drawings. But there was no more time to spare, the war was quickly deteriorating and the likelihood that any further German data would make it to Japan was incredibly slim.

U-234 surrenders, as seen from the USS Sutton.

Then, immediately following the capitulation of Germany, U-234 surrendered to the USS Sutton on the 14th of May, dashing any last chance for the arrival of German technology. Even as the captured German technicians expressed the notion that Japan would never be able to develop an Me 262 of their own without the onboard materials, the design of Karyū was nevertheless progressing, unknown to the rest of the world.

In the initial draft, Karyū had a conventional linear wing, with the airframe dimensions at a span of 12.56m and a length of 10.55m, a size nearly identical to the Me 262. Ultimately though, the airframe design settled on a shape that appeared closely to Me 262, with a larger footprint of 13.7m span and 11.5m length (a size exceeding Me 262, at 12.6m span and 10.6m length). Accordingly, the wings were swept, and the cross-section of the fuselage was distinctly triangular in the mid-section. A tricycle-type landing gear configuration was adopted. The engine selected was the Ne-230 turbine rocket, or alternatively the somewhat more powerful Ne-130, and one was suspended under each wing. Two 1,000kg gunpowder rockets installed under the fuselage would aid takeoff.

Karyuu June 1945 syllabus, highlighting the initial
requirements and many detailed specifications.

The basic design drawings of Ki-201 were finalized in June, almost perfectly to schedule. The basic shape of Karyū almost perfectly matches its parent, though it is considerably larger in dimensions. This was a sharp contrast to the Navy's 'Kikka', also developed at Nakajima — due to Kikka’s low thrust engines, it had to be designed as a very small aircraft to in order to be practical. On the other end, with the development of high-thrust turbojets as the engine for Karyū, the domestic production of a larger jet like ‘Me 262’ was possible for the first time. However, it was around this time that troubles with the development of these very engines delayed the projected completion of Karyū No. 1 to March 1946, with the full-scale mock-up to be reviewed in August of the preceding year.

The detailed design of Karyū was begun in June immediately after the basic stage was finalized. Though it bore an extremely similar resemblance to Me 262 externally, the detailed structure and materials were quite different due to the circumstances such as the lack of manufacturing plans and the severe material shortages at the time. Me 262’s construction had to be reverse engineered manually using Japanese methods without any detailed design prints. One could say that the typical Japanese method of aircraft design was incorporated into the shape of the Me 262 to create the Karyū.

Me 262 A and Ki-201 to scale.

Nakajima's original designs were applied in areas including the canopy, lateral shape, and vertical tail. The main aircraft material was the lightweight duralumin alloy SDH, and other materials such as silicon-manganese steel, carbon steel, and tin were used in various components on a smaller scale. Just like Me 262, the airframe structure is semi-monocoque, and the wings were of single-spar (with an 'auxiliary' spar) construction, with slotted flaps and leading-edge slats splitting around the engines. Two main fuel tanks of 1,200 litres were located in front and behind the cockpit, with a 600 litre auxiliary tank set behind the rear tank, for a total fuel capacity of 3,000 litres. All fuel tanks were self-sealing and the main tanks were equipped with automatic fire extinguishers. An 8mm steel plate is provided in front of the cockpit, with 8mm at the back and 12mm at the head of the seat. The front of the windshield is composed of 70mm of bulletproof glass.

Browning-derived Ho-155 Model II 30mm.

Compared to Me 262 A, Karyū mounted engines of roughly the same power while increasing the size of the airframe. As such, the maximum top speed estimated by the designers was somewhat lower, though curiously it was projected to exceed Me 262 at extreme altitudes when utilizing Ne-130 engines. Karyū’s increased wing area granted it a lighter wing loading and a higher estimated climb rate.

Me 262 A was well armed with a quartet of MK 108 autocannons in the nose for bomber interception, and Karyū, aiming to take down the B-29 bomber tormenting Japan, was similarly heavily equipped. The machine cannons on the lower outboard of the nose were 30mm caliber and the upper inboard two guns were 20mm. For the Japanese Army, these guns were the Ho-155 Model II & Type2 respectively, powerful cannons loading fuzeless shells able to down a heavy bomber in only a few hits. Both possessed a muzzle velocity roughly 200 m/s over that of the MK 108 and thus were more desirable for firing on air targets. Ki-201 would also be able to load a bomb as large as 800kg, larger than the fighter-bomber Me 262 A-2a’s maximum bomb load of 500kg, or a single 600l drop-tank for long-range missions. Radar ordnance consisted a Ta-Ki Mk. 15 Friend-Foe Identification Radar, and a Ta-Ki Mk. 13 Low-Altitude Altimeter, both stored behind the cockpit along with the radio.

The detailed design work on the Karyū continued throughout July, and basic aerodynamics examinations were completed together with the wind tunnel testing of scale models at around the same time. Construction preparations of the first prototype also began this month, immediately before the end of the war. With just five months lapsed from the start of the design to this point, the startlingly frantic pace of Karyū's development can be seen.

Ki-201 original design drawings.

Unfortunately for Japan’s Me 262, it was on August 15th that the end of the war finally arrived. Although design work had progressed at a remarkably fast rate for the situation at the time, development was canceled here and the project ended wholly incomplete. If any actual manufacturing of components apart from the mockup preparation took place, it was not significant enough for the airframe to begin any considerable level of assembly. The IJA’s first and last jet fighter, Karyū, never was to grace the skies over Japan. This anticlimactic ending is a simple reality of most advanced wartime projects. It was a wasteful act for the Navy and Army to order Nakajima to develop a jet aircraft inspired by ‘Me 262’ at the same time, and Karyū’s development suffered as a result. In the end, had efforts been focused on one aircraft, more progress could have been made.

The status points taken from data submitted by Nakajima Aircraft at the war’s end follow:

• About 50% completion of the design
• About 0% completion of the prototype
• Status:
• Started manufacturing full-scale mockup. 
• Only drawings complete at present.

Ki-201 prototype assembly status (center, 0%).

The principle of Karyū was to create a high-performance jet aircraft sporting a devastating offensive armament capable of taking down the American Boeing B-29, as well as having the capability to equip a large bomb to attack the US fleet. Additionally, it was aiming to confront the Allied jet aircraft of a similar role developing at the time, such as the American Lockheed P-80 & British Gloster Meteor, noted by Nakajima. The prototype was to have been assembled near the Mitaka Institute, at a large hangar originally built for the cancelled G10N "Fugaku" super-heavy bomber. The production of Karyū was scheduled to commence at the Nakajima Iwate factory, which was the dispersal factory of the Mitaka Institute.

The Mitaka Institute was remodeled into the International Christian University after the war, and the prototype Karyū's assembly-site-to-be is now occupied by only a thicket of trees.

The head of examinations for the Ki-201 prototype was scheduled to have been Major Yoshitsugu Aramaki.



Ki-201 Official Estimated Specifications (adapted from June & October 1945 data sheets)

Dimensions Full Width 13.700m Full Length 11.500m Full Height 4.050m Main Wing Area 25.0m2 Weight Empty Weight 4465kg Loading Weight 2497kg Normal Load 6962kg Special Load 8469kg Wing Loading 278.48kg/m2 Crew 1 (pilot) Fuel Capacity Normal Load 2,120l Special Load 2,590l Oil Capacity Normal Load 80l Special Load 100l Ordnance Guns [rpg] Ho-155 II 30mm x2 [120] Type2 20mm x2 [200] or Type2 20mm x4 [200] Bombs No. 50 500kg x1 or No. 80 800kg x1 Radar Ta-Ki 15 IFF x1 Ta-Ki 13 Low-Altimeter x1

Mounted Engine Ne-230 (885kgf) x2 or Ne-130 (908kgf) x2 Top Speed Ne-230 726 km/h @ SL 792 km/h @ 6,000m 812 km/h @ 10,000m Ne-130 740 km/h @ SL 811 km/h @ 6,0000m 852 km/h @ 10,000m Climb Rate Ne-230 18.9m/s @ SL 6’52” to 6,000m 10’18” to 8,000m 14’56” to 10,000m Ne-130 6’17” to 6,000m 13’15” to 10,000m Cruising Range 100% Thrust 794km @ 8,000m 80% Thrust 888km @ 8,000m 60% Thrust 980km @ 8,000m Practical Ceiling 13,600m Never Exceed Speed 1,000km/h Takeoff Normal Load Speed: 200km/h Distance: 949m Special Load Speed: 210km/h Distance: 1,580m Landing 5,300kg Speed: 158.5km/h Distance: 478m

Mitaka prototype factory hangar (centre-back) where the prototype Karyuu would have been assembled.

High-Power Engine Development for Karyū

Both of the engines scheduled for Karyū, Ishikawajima Shibaura Turbine’s Ne-130 and 1st Munition Arsenal (formerly Nakajima Aircraft)–Hitachi Work's Ne-230, were at approximately the same stage of development when the war ended. Neither were ready for use. The larger and heavier Mitsubishi Ne-330, as previously mentioned, wasn’t considered for the final Ki-201. It is quite remarkable that the Japanese were able to engineer these turbojets, most famously the smaller Ne-20 for Kikka, with little more than a cutaway of a BMW 003 and even less material availability than Germany.

Ne-130

The first unit of Ne-130 was completed at the end of May 1945, and the team at Tachikawa tested it as far as 8,000 RPM when the engine heavily damaged itself. The cause was hairline fractures in the construction of the compressor blades, which caused the blades to splinter off at high stress operation. The second engine was completed in early July and eventually successfully tested at full power in August. However, when testing again with accurate measuring equipment on August 16th, one day after the war’s end, the compressor blades were damaged by a foreign object being inhaled. Unit three was completed, but had been destroyed on August 2nd when the Tsurumi factory was bombed. As such, there ultimately were no functional Ne-130 engines in the possession of the Japanese.

Ne-130 Main Specifications:

• Dimensions:
• Length: 3850mm
• Diameter: 850mm
• Weight: 900kg (wet)
• Thrust: 908kgf 
• Revolutions: 9000rpm
• Configuration:
• 7 stage axial compressor
• annular combustion chamber
• 1 stage axial turbine
• Pressure Ratio: 3.56
• Fuel Consumption: 1.39kg/hr/kgf

Ne-230

The first Ne-230 was completed at Mitaka in March 1945. Unit two was finished in May, with the final unit in June. During the testing at Takahagi, while applying countermeasures for faults in the engine’s testing, it is said that the engines (a number or all) were damaged by a bombing raid. No engine was transferred to the US for testing after the war, and as such it’s fairly likely that no functional engine survived the war. In late 2017 the parts of two Ne-230 engines were found in the International Christian University, which was formerly known as the Mitaka Institute. The remains included two nozzles and a cover. There is a possibility that these were not ever part of a functional engine, as they show no obvious signs of being bolted to other pieces. Of the late engines, only Ne-230’s drawing is not present.

Ne-230 Main Specifications:

• Dimensions:
• Length: 3430mm
• Diameter: 762mm
• Weight: 870kg (wet)
• Thrust: 885kgf 
• Revolutions: 8100rpm
• Configuration:
• 7 stage axial compressor
• annular combustion chamber
• 1 stage axial turbine
• Pressure Ratio: 3.6
• Fuel Consumption: 1.84l/hr/kgf

In the end, the only successful Japanese turbojet to reach mass production was the less ambitious Ne-20. This engine was developed for the Navy’s special-attacker Kikka, and was smaller and less powerful than the engines for the Army’s fighter-attacker Karyū, providing only about 490 kgf of thrust. Development progressed quickly as a result, and Kikka flew for the first time in August 1945, the first and last Japanese turbojet aircraft to do so during World War II. From the simple Kikka to the ambitious Karyū, it could be said that the greatest driving force behind the jet development program in Japan was always the powerful inspiration of the 'Me 262'.

'Kikka' which unlike Karyuu, made it to the stage of test-flight. Though a rough resemblance
could be observed, this aircraft was not a copy of the Me 262, nor related to the Ki-201.

[Translation of Ki-201 "Karyuu" Airframe Manual Here]