Following the surrender of Japan in August 1945, the American occupational authorities sought to gather whatever aircraft developments were of potential interest. Naturally, the most cutting edge planes and engines developed in Japan were high on this list. More than a few of these projects had already been destroyed by Japanese orders immediately issued to prevent that from occurring.
None of the most powerful Japanese turbojets, Ne-130, Ne-230, or Ne-330, were left in Japan to recover. These prototype axial-flow jet engines were to be comparable in performance to the late German models, but each had been destroyed or hidden, one way or another, by September. Even the well known ‘Ne-20’, the turbojet of the Kikka, had risked destruction. The units under the Navy’s direct jurisdiction were sabotaged on such orders; luckily, a few survived at other organizations.
A couple of photos taken on October 16, 1945, show us some of the more obscure Japanese engines that were seized by the US. These photos display a group largely consisting of prototype jet engines awaiting preparation for shipment to the US by the 7th Air Service Area Command of the USAAF. The purpose of this article is to identify each engine shown in these photos and their subsequent fate.
Photos
Almost every engine visible and identifiable in this roundup was designed, if not manufactured, at the Navy 1st Air Technical Arsenal (Kūgishō). The Kūgishō was a center of Japanese jet engine development until the end of the war. Here, pioneering efforts led by Tokiyasu Tanegashima from the year 1941 resulted in a variety of test engines. Only in mid-1944 did the jet engine receive appropriate attention from the upper brass of the Navy, after which increased funding and restless development by Tanegashima’s group managed to yield the successful flight of Kikka with its twin Ne-20 turbojets just before the end of the war.
Engine Identifications – Left Side
‘Sakae IPR’ Blower
First on this list is a very obscure, almost unknown jet engine project. No doubt inspired by the engine of the Caproni Campini N.1 which flew in 1940, the ‘Sakae IPR’ was a motorjet using a Sakae Mod.11 piston engine to drive a five-stage axial blower, which was followed by a burner. ‘IPR’ stood for “Internal Propeller Rocket”.
It was one of the very first Japanese air-breathing jet engines, built during 1943. This engine produced 604 kgf of thrust, and had large dimensions of 4.17 m length by .91 m diameter. It was designed and probably manufactured at the Navy’s Kūgishō.
Only the blower seems to have been recovered at the time of this photo. Though the Sakae IPR blower was possibly transported to the USA, it was likely of little interest, and no piece of it is known to survive today.
Ne-12
Next we have the Ne-12B, the last model in the original series of Japanese turbojets. This was a follow-on design to the original centrifugal ‘Ne-10 series’ turbojet. The four-stage axial compressor, clearly visible in this photo, leads into the main centrifugal compressor.
The Ne-10 Kai was the first model to implement this axial compressor, followed by the Ne-12 which featured reinforcements to improve durability and features for fixing to an aircraft. The final Ne-12B was a model which lightened the weight of the Ne-12 by as much as 70 kg. It is most likely that the engine in this photo is in fact the Ne-12B based on the date, but the visual differences from Ne-12 are unknown. All of these engines were designed at the Kūgishō.
The Ne-12B had a weight of 315 kg and dimensions of 1.80 m length by .86 m diameter. It ran at 15,000 rpm and aimed to produce 320 kgf of thrust. This engine only was able to demonstrate a lifespan of perhaps 1 hour by the end of the war, and had been abandoned in April 1945 after a production run of 12 units, split between the Kūgishō and the Yokosuka Arsenal.
This is, to my knowledge, the only known photo of the Ne-12/B. The engine did not survive to this day, but the 1st stage of a Ne-12B axial compressor is displayed at the National Museum of Nature and Science in Tokyo.
YE3B
Behind the Ne-12 is not a jet, but the YE3B piston engine, a very unusual design. This is a 24-cylinder liquid-cooled engine of the X arrangement, which aimed to produce 2,500 horsepower. It had been abandoned by the end of the war per US intel in favor of the YE3E, a 3,200 horsepower development of the same engine.
Based on very little documented data, the YE3B had cylinders with 145 mm bore and 160 mm stroke. The total displacement was 63.4 liters. It was designed and built by the Kūgishō. In this photo, the engine faces with the back side towards the camera, featuring the supercharger. The upper left row of cylinders and exhaust pipes are visible.
The engine survives today in storage under the ownership of the Smithsonian. Dimensional data of 2.29 m length by 1.75 m width is provided, which contrasts with the (likely erroneous) documented US data of 1.10 m length.
Tsu-11 / Hatsukaze Rocket
The small piston engine here is actually part of a jet. This is the ‘Hatsukaze’ engine portion of the ‘Hatsukaze Rocket’, a Japanese informal name of the Tsu-11 motorjet. Only the Hatsukaze itself is visible in this photo, but based on later photos, it can be confirmed that this is a Tsu-11 setup.
The Tsu-11 consisted of a Hatsukaze piston engine driving at 3,000 rpm, which was stepped up to 9,000 rpm to rotate a single-stage axial fan, followed by a burner. The overall setup weighed 200 kg and produced a very modest 220 kgf of thrust. The dimensions were 2.20 meters length by .64 meters width. Tsu-11 was designed by the Kūgishō but produced at Hitachi Aircraft.
This engine was only ever fitted to the Ōka Model 22 piloted missile, and the ‘Ginga’ bomber as a test auxiliary power unit. It had been contemplated as a temporary engine for the Kikka (in a quad installation of two per wing) if the main turbojets were not ready in time. The performance was very poor, the engine could not be started in the air, and would spontaneously seize at altitudes higher than around 4,000 meters. It did, however, provide the Ōka with a better standoff range than the previously used rocket engines. This would have improved the survive-ability of the mother plane, but perhaps not the missile itself.
A Tsu-11 survives today, installed in the sole Ōka Model 22 preserved at the Smithsonian National Air and Space Museum.
Unidentified
The last two clear objects in this photo I have not identified, although it should be possible. These are a radial engine and an unknown engine to the right of it with an exposed propeller fitting, sitting behind the IPR blower and the Ne-12. If you can help identify these, you could leave a comment on this post.
The rest of the engines to the lower right of the whole photo are not included in this section, as they are more clearly visible in the right-side photograph.
Engine Identifications – Right Side
Ka-10 / Maru-Ka, & Small Model
Here is not only the Ka-10 pulsejet (also named ‘Maru-Ka’ ㋕), but almost hidden behind it, its smaller initial prototype version. These were the only pulsejets built by Japan during World War II. They were directly based on the German As 014 pulsejet used to power the V1 flying bomb.
The full-sized Ka-10 had dimensions of 3.70 meters length by .58 meters width, weighed 150 kilograms and was designed to produce 300 kilogram-force of thrust. The specifications of the smaller test version are unknown.
According to Japanese records, the small test model was completed in early 1945 and tested until June; the full-sized version followed it at the end of July, and remained under testing when the war ended in August. According to a member of the Army special weapons team, five units were built. This engine was to power the ‘Baika’: an ultra low-cost, manned flying bomb designed by Kawanishi Aircraft, which was similar in concept to the Fieseler Fi 103R ‘Reichenberg’, though somewhat more sophisticated in airframe design. However, the Baika had only lapsed one month of design progress when the war ended.
These are the only known photos of the Maru-Ka, which does not survive to this day.
KR10
To the right of the Maru-Ka is the rather well known KR10 liquid-rocket engine, which powered the Shūsui, Japan’s version of the Me 163B Komet rocket interceptor. Technically speaking, this could be the variant ‘KR20’, or ‘KR22’, which differed by thickening the turbopump shaft or increasing its structural support respectively. It is impossible to determine from this photo, but all versions of the engine are typically referred to as ‘KR10’ informally.
KR10 had dimensions of 2.52 meters length by .90 meters width, and weighed 170 kg. It produced 1500 kilogram-force of thrust, identical to the initial model of the German Walther HWK 109-509. The liquid fuel used consisted of the ‘Kō’ and ‘Otsu’ liquids, analogous to the ‘T-Stoff’ and ‘C-Stoff’ used in Germany.
The engine was designed by the Kūgishō with contribution from Mitsubishi, and was manufactured at the Kūgishō and various naval arsenals. The engine ‘KR22’ made by Hiro Naval Arsenal was the unit actually fitted to the Shūsui which flew on July 7th, 1945. This flight met with failure and death of the pilot due to the layout of the fuel system, which failed to feed with a reduced fuel load in a steep climb angle.
Ne-20
The Ne-20 turbojet is the most famous Japanese jet engine from World War II. It is typically referred to as “the first Japanese jet engine”; though it was not the first built by any measure, it is true in the sense that it was the first successful unit.
This engine was designed at the Kūgishō under the leadership of Osamu Nagano. Ne-20, based on the BMW 003A format, had an incredibly rapid developmental pace – advancing from merely a concept to an initial prototype in only three months, and passing trials in another three. Due to this impressive feat, the special attack plane ‘Kikka’ was able to successfully fly on August 7th, 8 days before the end of the war.
Ne-20 had dimensions of 2.70 meters length by .62 meters diameter. It weighed 470 kilograms, rotated at a maximum of 11,000 rpm, and produced thrust from 475 to 490 kilogram-force. The prototypes and first production engines were built at the Kūgishō, with additional production units being made at the Yokosuka Naval Arsenal. Around 20 examples are known to have been completed in total.
The engine in this photo appears to be marked ’19’. Perhaps this was the 19th engine, one of the production examples built at the Yokosuka Naval Arsenal. Some of these engines had been rejected due to poor workmanship related to the lack of experience building jets at the naval yard.
Three Ne-20 turbojets survive to this day: two at the Smithsonian National Air and Space Museum (one on display), and the other example at the Ishikawajima-Harima company museum.
‘Ne-201’ or ‘GTPR’ Turbine-Nozzle Mockup
The Ne-201 and the GTPR are practically unknown engines, especially in English sources. These were both turboprops, designed by the Army and Navy respectively from about the same time (~1942).
Ne-201 was designed by the Kogiken (Army Aero Tech Lab) and Kōken (Tokyo Imperial Uni Aero Dept), manufactured by Ishikawajima Shibaura Turbine. GTPR was designed at the Kūgishō, to be manufactured by Ishikawajima Shibaura Turbine as well. GTPR stood for ‘Gas Turbine Propeller Rocket’.
Both of these engines have been listed here due to the ambiguity of their history. I can state with certainty that the Ne-201 and GTPR were, at the outset, independent projects. However, a few accounts from first-hand suggest that they were the same thing, and a US report identifies this mockup as the ‘GTPR’ component, even though it almost exactly matches a known ‘Ne-201’ design drawing.
Currently, I’ve theorized that at the time of August 1944, when jet development between the Army and Navy was unified, the more developed turboprop project was probably taken (Army Ne-201), but placed under unified leadership. Thus, what was once just Ne-201 likely came to be known by either designation, and developed a bit further until the end of the war.
Ne-201 had been built in 1944, and the original GTPR was ordered but never completed. Both designs were to be converted to turbojets in 1944, as priority was placed upon that type of engine, but ultimately Ishikawajima Shibaura Turbine created the turbojet ‘Ne-130’ from scratch. In December 1944 the Ne-201/GTPR damaged itself, by April 1945 it was ready for a re-test, but due to focus on the Ne-130 it received little attention until the end of the war.
Ne-201 had dimensions of 5.75 meters length by 1.10 meters diameter, and weighed 2,500 kilograms. It rotated at 4,200 rpm and produced 862 kilogram-force of thrust (prop 1870 shp/280 kgf + 582 kgf exhaust thrust). An iteration of the GTPR had dimensions of 5.50 meters length by .85 meters diameter and weighed 2,500 kilograms. It rotated at 5,000 rpm and aimed to produce 5,000 equivalent horsepower.
After the war, Tanegashima prepared a report on the GTPR for the US, although the details he provides are unlike either design. It is likely that as a personal passion project, he continued to work on the GTPR design aside more pressing matters until the end of the war, incorporating data learned from BMW 003A and Ne-20.
This turboprop mockup did not survive to this day.
Ne-30 & Ne-30 Mockup
The Ne-30 was one engine in the initial ‘Ne-10 series’ of Navy turbojets. It was a unique departure as an attempt to gain high thrust from the relatively low-performance engine design by upscaling it in size. Effectively, this was a larger Ne-12, with the same features. The left engine installed on a stand is the actual prototype, while the object to the right is the mockup. “Mock of TR30” is possibly written on the side.
The Ne-30 had dimensions of 2.47 meters length by 1.03 meters width, and weighed 900 kilograms. It rotated at 15,000 rpm and aimed to produce 850 kilogram-force of thrust. It was designed by the Kūgishō and built there in November 1944. However, the Ne-30 never demonstrated its intended performance and was abandoned, as with the other Ne-10 series engines. This engine had been contemplated as the original engine of the R2Y2, Keiun Kai, and the Tenga, a jet-version of the Ginga bomber.
Both the engine and its mockup were brought to the USA and still remain in the storage of the Smithsonian today.
Ne-10 & Ne-10 Exhaust Nozzle
This engine on the right seems to be the Ne-10, the first functional Japanese turbojet. This can be deduced by the apparent lack of axial compressor stages extending from the front side (which faces away from the camera). The visible side is the turbine at the rear.
The design of the entire Ne-10 series was, put simply, a huge turbocharger converted to a turbojet by installing a folded combustion chamber. First built in mid-1943 as the ‘TR’ (Turbine Rocket), the design was renamed ‘TR10’ in 1944 and prepared for mass production to perform trial-and-error testing. By the end of 1944, it had again been renamed as the ‘Ne-10’ due to unifying development with the Army, which created shared nomenclature.
On the left is presumably the exhaust nozzle to produce thrust from the Ne-10. You can see the attachment points both on the edges of the nozzle and the engine, circling the turbine. An early problem with the Ne-10 had been the nozzle warping into the turbine under heat due to a lack of resistant materials.
Ne-10 had dimensions of 1.60 meters length by .85 meters diameter. It rotated at 16,000 rpm and was designed to produce 300 kilogram-force of thrust. It was designed by Tanegashima’s group at the Kūgishō and only a handful were built, perhaps less than ten. It is somewhat surprising that an original Ne-10 survived to the end of the war, as these engines had a very short lifespan, and a tendency to fail disastrously.
No example of the Ne-10 survived to this day, nor any known components.
YE2H
Lastly, this engine is rather hard to spot. Behind the Ne-10 nozzle is the YE2H prototype – an 18-cylinder, liquid-cooled piston engine of the W-layout. Luckily, a view from the same side of the surviving engine provided by the Smithsonian shows identical features which can be compared to this image.
YE2H has dimensions of 2.46 meters length by 1.12 meters width, and weighs about 1,200 kilograms. The cylinders had the same 145 mm bores and 160 mm stroke as the YE3B shown prior, with a 47.5 liter total displacement. YE2H was to produce 2,500 horsepower. It was designed and built by the Kūgishō, and undergoing a breakdown test there when the war ended.
As mentioned, the YE2H survives today in the storage of the Smithsonian.
Photo: Smithsonian
Unidentified
The only object I cannot readily identify in the right-side view is this large jet exhaust nozzle. It is clearly considerably wider than the exhaust nozzle of the Ne-20 in the foreground, and even the centrifugal Ne-10. Unlike known exhaust sections from larger Japanese jets, the exit cone protrudes far from the end of the nozzle. It does not appear to be the exhaust nozzle for the Ne-30, nor Ne-130, or Ne-330.
I have speculated that this could be the turbine and exhaust section of the Ne-140, which was the huge turbojet converted from the GTPR turboprop design. However, it is unlikely that any part of the Ne-140 was built before development was apparently terminated in late 1944 or early 1945. The only source (of few overall) that contradicts this is Senshi Sōsho 87, which suggests that Ne-140 was tested by the end of the war, although I suspect that this is a mistake.
Alternatively, it could be possible that this is the turbine and exhaust nozzle of the MTPR, a compound “engine-turbojet” consisting of an Atsuta (DB601) piston engine which drove a prop, and also transferred some power to the compressor of a turbojet linked to it. According to limited information, MTPR was under construction from 1943 before being canceled in mid-1944.
*July 9th 2023: Correction on completion/test dates of Maru-Ka
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