Kōgiken-IST Ne-130: Driven to Destruction After the War

On July 26th, 1944, the Japanese Navy submarine I-29 ‘Matsu’ was sunk by the USS Sawfish near the Philippines while en route to Kure. Onboard ‘Matsu’ were potentially instrumental materials about secret German aircraft technology. Of relevance, there were survey sketches and other data on the Messerschmitt Me 262 and Me 163 and actual examples of their respective jet and rocket engines.

Not all the data was lost, as Navy attaché Technical Commander Eiichi Iwaya had departed the submarine with some of the materials while it was docked at Singapore on July 14th. He boarded a Type 0 Transport Plane on the 17th for a flight to Japan and arrived at Haneda on the 19th. He reported to the Navy Air HQ and then traveled to the Navy 1st Air Technical Arsenal (Kūgishō) where a study meeting was held.

The materials Iwaya brought were a single 1/15th-reduced side diagram of the BMW 003A turbojet, observation notes on the BMW and the Jumo 004B turbojet, construction drawings of the Walther liquid rocket engine, and operation manuals for the Me 262 and Me 163 fighters. The fine details on the BMW 003A diagram were impossible to see when blown up to a useful size, so questions were telegrammed to another Navy attaché stationed in Germany.

A joint study meeting was subsequently held at the Kūgishō on July 27th between officials of the Navy, Army, and six private companies that had been ordered to produce jet engines. Before this point, the development of jet and rocket engines had been conducted independently by both military branches, without sharing research, while ordering the same manufacturers. With the declining war situation causing a scarcity of materials and time, they now had no choice but to collaborate.

(Note that the following history is constructed largely from the recollections of those involved, rather than historical documents, of which very few survive.)

Turboprops-turned-Turbojets

As a result of the joint meetings, which also took place in August and September, the division of work between both military branches was decided. The Army, probably because of their ‘Toku-Ro Mk.1’ liquid rocket already under development, was to oversee the development of liquid rockets, and the Navy was similarly to oversee the development of jet engines. To this end, the Army’s previous series of jet engines was entirely canceled.

However, both the Army and Navy each had a turboprop engine also under development at the time. The Army’s was the ‘Ne-201’ (planned output: 1,870 shaft horsepower + 582 kg thrust), and the Navy’s was the ‘GTPR’ (planned output: 3,000 shaft horsepower + ~700 kg thrust). Both of these turboprops had been ordered to be constructed by Ishikawajima Shibaura Turbine. But with the focus now heavily shifting to the turbojet format after the arrival of the BMW diagram, the Navy ordered the conversion of the GTPR to a turbojet named ‘TR140’, and the Army also ordered the design adaption of the Ne-201 to a turbojet called ‘Ne-201II’.

It was decided at these meetings that three private company groups would develop new turbojet engines of a high output suitable for fighter planes, overseen by the Navy. The TR140 was naturally the responsibility of Ishikawajima Shibaura Turbine, while Nakajima Airplane Company and Hitachi Aircraft Company were assigned the ‘TR230’, and Mitsubishi Heavy Industries along with Niigata Ironworks were assigned the ‘TR330’. The latter two engines were from scratch, based on the BMW 003A’s diagram.

(The names of all turbojet engines were supposed to be standardized to the Army’s prefix of ‘Ne’ at this time, rather than the Navy’s ‘TR’, but it took a while for the Navy to actually start using this change in practice.)

It seems that the development of the TR140 proceeded at Ishikawajima Shibaura Turbine for a few months, and was still the definitive engine planned by Ishikawajima until the end of September, but for unknown reasons, it was canceled by December 1944.

It was decided instead that the Army’s 2nd Air Technical Research Institute (henceforth: Nigiken) would take charge of the development of an engine based on the BMW 003A named ‘Ne-130’ in collaboration with Ishikawajima Shibaura Turbine. Inheriting the design experience of ‘Ne-201II’ and ‘TR140’, the project was set into motion at the end of 1944, trailing behind the other jet engines developed by the Navy and private companies.

The Development of ‘Ne-130’ by Young Engineers

The meeting to establish the basic design policy of the Ne-130 engine began at the Matsumoto dispersal site on December 13th, 1944. Present were members of the Nigiken, including the head of the institute Lieutenant General Enozawa, Engineer Kaneko, Lieutenant Colonel Kihara, and five young engineers: Colonel Okazaki, Colonel Harada, Colonel Akiyaka, Colonel Maeda, and First Lieutenant Nakamura.

“For me, I was just shocked. It was a truly terrifying order that told all of us young people to develop an engine more than two times as powerful as the Kūgishō [TR10] that was shown to us the other day.”

Yoshio Nakamura, Kuruma yo Konnichiwa Turbo-Jet. Ne-130

Under the guidance of professors from the Tokyo Imperial University Aviation Department who had researched the jet engine for years, Professor Nakanishi, Assistant Professor Awano, and Assistant Professor Hatta, the basic design targets of the engine were decided on December 15th after discussing the compressor, combustor, turbine and other aspects. The pressure ratio was to be 3, the number of revolutions at full power 9,000, flow volume 22.8 kg/s, maximum static thrust 900 kg, weight 900 kg, and turbine inlet temperature 750 °C.

After the basic policy meeting, the engineers from the Nigiken and Ishikawajima Shibaura Turbine grouped up at the Ishikawajima Shibaura Turbine Tsurumi Factory, where the basic and detailed design work on the Ne-130 was conducted. The division of development leads was as follows:

2nd Army Air Technical Research Institute Team:
Captain Taku Okazaki – Whole project and the turbine.
Captain Akiyama – Compressor and combustion chamber.
Lieutenant Yoshio Nakamura – Auxiliary drive and fuel system.
Captain Harada – External affairs with the Army Institute and Army Aviation HQ.
Captain Maeda – Internal affairs and test coordination with labs of the Army Institute.

Ishikawajima Shibaura Turbine Team:
Toshio Dokō – Company president, directing overall.
Mr. Ogura – Design lead.
Mr. Matsui – Turbine.
Izumi Iguchi and Mr. Enjōji – Compressor.
Ōmi Kishi – Auxiliary mechanisms and casing.

However, this division of work was only official, and at night in the Tsurumi dormitory, ideas were freely exchanged from all sides.

While the Ishikawajima Shibaura Turbine engineers were experienced with the development of steam turbine engines, this did not translate perfectly to aero engines, which use lighter and more streamlined construction, so the role of the Army in developing the design was crucial. Even the president of the IST company, Toshio Dokō, took part in the design discussions at times and often warned the young engineers “Don’t work yourselves too hard”, worrying about their health. Nonetheless, with a monumental effort, the design drawings of the Ne-130 were completed at the end of January 1945. The process was about a month and a half.

Around this time, the Army’s group from the Nigiken was reorganized into the “Army Special Weapons Department”.

The Ishikawajima Shibaura Turbine wooden models shop did not have experience in making fine models for aircraft engines, so the making of the Ne-130’s wooden mockup parts was outsourced to about 10 small wooden model shops distributed around the Fukagawa area. In many cases, dimensional errors were found in the drawings due to the very rushed work, but these were quickly corrected, and the wooden models were completed swiftly around the time of February 1945.

The first prototype of the Ne-130 was scheduled to be completed at the end of March 1945, but the Tsurumi factory experienced a significant degree of absenteeism around this time due to the start of B-29 strategic bombing raids in the area. The first unit was finally assembled in late May and delivered to the Army Special Weapons Department at Tachikawa.

A static running test of the engine was conducted on June 26th using a modified test stand originally for piston engines. When the test run began, the first failure was in the auxiliary mechanism drive due to a design flaw. After that, the engine was successfully raised to 8,000 RPMs for about one minute until a failure occurred in the compressor. The blades of the first axial stage shattered off and broke the blades of the second stage, continuing on to damage the rest of the stages. The Ne-130 was heavily damaged.

The cause of the failure was deemed to be a hair fracture that occurred during the creation of the blades. Luckily, there was no damage to the combustion chamber or turbine, but the damage was severe and would take considerable time to repair. It was decided that testing would continue when the second prototype was completed, and the first engine was sent back to the Tsurumi factory for repairs. The design of the compressor blades was strengthened to prevent future accidents.

Evacuation to Matsumoto

By mid-1945, the B-29 strategic bombing raids over Japan had intensified to a terrible degree. Much of Tōkyō and the surrounding region had been reduced to a charred wasteland. The engineers knew that Japan’s defeat was only a matter of time. Any day, the lab at Tachikawa could be hit.

In this situation, a meeting was held at the Tsurumi factory to decide where the Ne-130 project would be evacuated to continue development. It was supposed to be a joint meeting between the Army and Navy, but because of a bombing raid just prior, the higher ranking Army officials were not able to attend, and all of the ‘brass’ was on the Navy’s side. The young Army engineers could not speak from a place of authority.

The Navy had already evacuated the development of their jet engine, the ‘Ne-20’ to Hadano, Kanagawa prefecture at this time. In order to consolidate work on jet engines, they wanted to move the Ne-130 work to Hadano as well, and have the Navy’s jet department take over. The Army engineers, having come this far, were not pleased with the proposal, and nervously appealed to be able to evacuate to Matsumoto with the engine, where Ishikawajima Shibaura was also located.

Only one Navy official would understand the request. It was Technical Lieutenant-commander Osamu Nagano, the lead designer of the Ne-20 engine. He understood the connection between the young engineers and their engine, having also struggled with the hardships of a pioneer in the same technology himself.

“This should remain entrusted to the young men of the Army.”

Lt. Cmdr. Osamu Nagano, quoted in Jetto Enjin ni Toritsukareta Otoko

Encouraged by Nagano’s support, the Ishikawajima Shibaura team spoke up, insisting that their work would suffer if separated from the Army after cooperating for so long. Because of Nagano’s experience, the proposal to evacuate the Army’s team to Matsumoto was accepted.

The dispersal of the team and engine was completed by early July, and testing started at the schoolyard of Meidō Industrial School with the second prototype of the Ne-130. Testing was smooth as far as 6,000 RPMs, but above that many issues would occur such as the malfunction of the auxiliary drive gear bearing, oil leaks, damage to the fuel pipe or failure of the jet cone.

Technical Captain Tokiyasu Tanegashima, the pioneer of jet development in the Navy, visited the test site of the Ne-130 one day in mid-July. At this time, the team managed to reach a state of steady operation at 8,000 RPMs with the engine. Tanegashima walked to the rear of the engine and threw small pebbles behind the exhaust nozzle. The pebbles were blown far away by the jet, and he smiled.

Driven to Destruction After the War

In early August, the full-power test of the Ne-130 was achieved when the engine reached the design point of 9,000 RPMs. The flow rate, compression ratio, and thrust were observed to almost meet the designed values, but before it was possible to measure adequately, part of the measuring apparatus broke.

The part was repaired by August 14th, but the end of the war occurred the very next day.

On August 15th at noon, the Army Special Weapons Department at Matsumoto heard the ‘Jewel Voice Broadcast’ announcing the surrender of Japan on the radio. Nobody could quite understand much of what was spoken, but it was clear that Japan’s defeat in the war had come.

The head of the department, Mr. Ōtsubo, fell to his knees and began crying at the revelation of defeat. Gathering himself together, he announced that he planned to deny official orders and occupy the Army facilities in the districts of Tachikawa and Fussa to fight to the end. He ordered the officers to gather at the school grounds by 5 pm, but it seems that the resistance was not carried out in the end.

The jet team gathered separately and discussed what to do. The orders from the Ministry of Munitions were to destroy the Ne-130 and all related materials immediately. Everything had come to an end, but the Ne-130 was repaired, so why not have one last run?

With the intent being to run the engine at maximum power until it was destroyed, the final bench test was started on August 16th. However, before the engine was completely destroyed, a foreign object was sucked into the intake and damaged the blades. After that, in compliance with the orders, the materials related to the Ne-130 were incinerated, and the engine was hidden in a hillside tunnel somewhere in Nagano prefecture and sealed off.

The first and third prototypes of Ne-130 had been destroyed when the Tsurumi factory was destroyed by bombing on August 1st, leaving no engine intact for the US occupational forces at the end of the war.

Ne-130 Design and Specification

As previously mentioned, the Ne-130 turbojet was designed by the collaboration of the Army’s Nigiken and the Ishikawajima Shibaura Turbine Company, based mainly on the layout of the German ‘BMW 003A’ turbojet’s side-view. It was derived from the BMW 003A, but the actual engine had a larger size and higher performance target.

While the Nigiken group did not have in-depth experience with the design of jet engines and was composed of young engineers only a couple of years graduated, concept guidance was initially given by professors of the Tōkōken. The Ishikawajima Shibaura Turbine company side had experience with the design and manufacture of land-based turbine engines, and several gas turbines ordered by the Army and the Navy previously. The design of ‘Ne-201II’ was inherited, along with the ‘TR140’.

Compressor

The basic compressor format consisted of 7 axial rotor stages surrounded by 10 stators, adapted from the BMW 003A. The inner diameter ranged from 504 to 584 mm, and the outer diameter was 650 mm. The first stage had 36 blades.

The maximum rotational speed was set at 9,000 RPMs, intended to achieve a flow mass rate of 22.8 kg/s and a pressure ratio of 3.56 at static conditions. This is higher than the BMW 003A’s flow mass rate of 19.3 kg/s and pressure ratio of 3.1.

The compressor’s degree of reaction was 50%, which is lower than most of the other gas turbines ordered to Ishikawajima Shibaura Turbine around that time, Kō Mk.7, Ne-201, and GTPR, which had about 100% degree of reaction, but higher than the BMW 003A’s 30% reaction. The Navy’s Ne-20 turbojet compressor also had a 100% degree of reaction.

The compressor absorbed 4,155 HP from the turbine and had a planned efficiency ratio of 83%. From compressor testing after the war, it was found that the Ne-130’s compressor type probably had an actual efficiency of about 80%. The efficiency is therefore about the same as the BMW 003A’s (78 – 80%), and higher than Ne-20’s (73%).

Combustion Chamber

A cannular and annular-type combustion chamber were both experimented with. Both types had 12 fuel injectors and were made of 18-8 stainless steel.

The BMW 003A employed an annular combustion chamber, and this seems to be the type that was primarily tested on the Ne-130. However, thorough experiments to determine the efficiency of each combustion chamber type do not seem to have been conducted by the end of the war.

Turbine

The turbine format was of the axial single-stage, which was the standard of jet engines at that time. A diaphragm was positioned in front of the turbine to increase efficiency.

Each of the 80 turbine blades was firmly welded to the disc, using a method developed by Hitachi for turbochargers. This was less robust than the innovative ‘Christmas Tree’ slotted blade roots developed by Frank Whittle’s team in Britain. Unlike the BMW 003A, which used hollow air-cooled turbine blades, the turbine blades of the Ne-130 were solid.

At 9,000 RPMs, the Ne-130 turbine produced 4,390 HP. Due to the low strength of materials available under wartime conservation, the turbine inlet temperature was 750 °C. This is somewhat higher than the 700 °C inlet temperature of Ne-20, allowed by the lower rotational force exerted on the turbine compared to Ne-20’s 11,000 RPMs. The material used for the turbine was likely I-309, a stainless steel alloy composed without nickel.

Considering the low durability of materials, this was probably a turbine with a very low degree of reaction, allowing a thicker blade profile for strength.

Conclusion

The Ne-130 turbojet has a rather obscure place in the history of Japanese engine technology. Not unreasonably so: while the Ne-130 was one of the most powerful engines actually built by Japan during World War II, it was also only experimental, uncertainly far from the stage of practical use, and destroyed with little trace for the US occupation to recover.

Nonetheless, the story of the engine was a considerable achievement.

When it comes to Japanese jet engines from that era, the only model given a wide coverage (in any language) is the ‘Ne-20’ made by the jet engine group at the Navy’s Kūgishō. The Ne-20 was the only practical Japanese turbojet engine and had an astonishingly quick development time — 3 months from the start of design to a prototype, and another 3 months until it was cleared for service. It is regarded as one of the great technological feats of the time and was considered “doubtful” by the analysis of the US occupation side.

The young engineers of the Army’s Nigiken were given an order to supervise the development of an engine almost twice as powerful as the Ne-20, more ambitious than the original German ‘BMW 003A’, without the prior experience of the Navy. And even so, the initial development pace of the Ne-130 was not dissimilar to that of the Ne-20. The entire design was completed in just 1.5 months, and the first prototype could have been ready as early as March, the same month that the first Ne-20 was completed.

It is a testament to the persistence of the engineers at the Nigiken and Ishikawajima Shibaura Turbine that the Ne-130 was able to exhibit its full power operation before the end of the war. They knew the hopelessness of the situation, but their efforts would have been instrumental for the next generation of a fighter plane.

According to the recollection of Yoshio Nakamura, a Ne-130 was sealed in a tunnel in the Nagano prefecture after the end of the war. There remains the uncertain possibility that this piece of history may exist, in some form, today.

Sources

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