The Funryu (1JN)
The Funryu (‘Raging Dragon’) was the name given to the UN’s missile program that commenced in 1943. The initial study for the Funryu was conducted by the Kaigun Gijyutsu Kenkyujyo (Navy Technology Laboratory) but three other groups would review the study soon afterwards and they were the Dai-Ichi Kaigun Koku Gijutsu-sho, Dai-Ni Kayaku-Sho (2nd Bureau of Gunpowder) and the Kure Kosho (Kure Arsenal). Ultimately, it would be Kugisho that was given the Funryu project in early 1944. To accomplish the task, Kugisho formed the Funshin Kenkyu-Bu (Rocket Research Bureau) and was staffed with up to 200 technicians led by a research team made up of 40 officers (all engineers and/or technicians) from the UN. In all, Kugisho would investigate and put forward four Funryu designs.
The first was the Funryu 1 and the design was an air-to-surface missile (ASM) whose specific role was anti-shipping. Funryu 1 was much like a miniature airplane. The warhead contained 8821b of explosive and guidance was via radio control. Testing of the Funryu 1 was conducted with the missile being dropped from a modified Mitsubishi G4M bomber. However, it was seen that the means to effectively control the missile in flight would require a significant amount of time to perfect and with the increase in US bombing raids against Japan, it was decided that efforts should be directed towards sur – face-to-air missiles (SAMs). Thus, the Funryu 1 was shelved and was to be the only ASM of the Funryu family.
The Funryu 2 was to be a SAM built around a solid fuel rocket using a radio guidance system. Despite three rocket motors being available already (the Ro-Tsu, Ro-Sa and Ro-Ta), it was decided that a new motor was required. This motor was capable of producing 2,400kg (5,291 lb) of thrust during its 3.5 second burn time. The shape of the missile was relatively simple. Four wooden wings were fitted to the body of the missile and each was equipped with an elevon (elevons control both pitch and roll). Four fins, making up the tail, were fitted to the outside of the nozzle for the motor. This final shape and configuration was a result of numerous tests of various missile bodies and wing/fm arrangements in a wind tunnel. The radio guidance system was initially to consist of a single transmitter but a second was fitted to ensure a measure of accuracy. The first transmitter was used for target detection while the second would control and steer the missile to the target. To maintain attitude, the Funryu 2 contained two gyrocompasses and 50kg (1101b) of explosive was housed in the nose. The basic operation consisted of the Funryu 2 being launched from a rail set at an angle of 80°. Once launched, radio receivers fitted in the wings would receive signals from the ground transmitter, steering the missile onto the target.
The war situation in 1944 was starving Japan of critical war materials and KQgisho found they were unable to obtain the necessary quantity of duralumin to build the Funryu 2 prototypes. It took theft from a warehouse to obtain the required metals. Using the absconded material, a number of Funryu 2 missiles were constructed with one being used for continued wind tunnel testing and the remainder used for actual field tests, the latter being conducted near Mount Asama (located near Ueda). Testing commenced in the spring of 1945. The first launches of the Funryu 2 were unguided, conducted solely to evaluate the rocket motor performance and the general flight characteristics of the missile. In July 1945, the first test of the Funryu 2 was undertaken using the radio guidance system. With UN personnel in attendance, the Funryu 2 successfully lifted off from the launch rail and was directed towards a ground target. Using the radio signals, the Funryu 2 was guided to within 20m (65ft) of the target when impact was made. Although a direct hit was not achieved, the test was considered a success. It was to be, however, the last flight of the Funryu 2 because the war ended before any further launches could be made.
The Funryu 2 was 2.2m (7.2ft) long, ,28m (0.9ft) in diameter and had a span of.88m (2.9ft). Total launch weight of the missile was 370kg (8161b) and its maximum ceiling was 5,000m (16,404ft). The maximum speed of the missile at full burn was 845km/h (525mph).
Even as the Funryu 2 was being investigated, a variant of the missile, the Funryu 3, was proposed using a liquid fuel rocket in place of the solid fuel motor. However, initial discussions on the new rocket engine led to the conclusion that there was no time or resources available to study, design, construct and test such a propulsion method. As such, the Funryu 3 was shelved.
With the commencement of flight testing of the Funryu 2, work got underway on another SAM that was to be far more advanced. This missile was designated the Funryu 4. Design work was carried out by engineers from Mitsubishi and from the Aircraft Equipment Factory of Tokyo, all based in a facility in the Izu Peninsula, west of Tokyo. The Funryu 4 was to be built around the Toko Ro.2 (KR10) rocket engine, the very same engine used in the Mitsubishi J8M Svusui rocket fighter. As testing of the Toko Ro.2 was already underway and would soon be put into production, Mitsubishi could devote less time to engine concerns. The Funryu 4 was to use a mixture of the Ко fuels (concentrated hydrogen peroxide) and Otsu (hydrazine hydrate solution in methyl alcohol) as used by the J8M. The engine would provide up to 1,500kg (3,307 lb) of thrust and move the Funryu 4 to a maximum speed of l,099km/h (683mph).
The guidance system selected for the Funryu 4 was far more sophisticated than that used in the Funryu 2. Whereas the latter relied on radio, the Funryu 4 would use radar. Two stations would be used to deliver the Funryu 4 to the target. One station would track the target while the second would track and control the missile. The intention was that the two radar signals would coincide on the target, thus bringing the missile to impact. To control the missile, a radio signal of 1,000MHz was to be used with five frequencies. Each frequency corresponded to controlling the pitch and the roll with the fifth being the detonation command. A variation of this system is used today known at retransmission homing or Track-via-Missile (TVM).
Funryu 4, like the Funryu 2, used two gyrocompasses and carried wing radio receivers for the commands sent to it from the ground. It carried a far heavier warhead of 200kg (4401b) in comparison to the 50kg (1101b) warhead of the Funryu 2. The shape of the Funryu 4 was also more streamlined and it only had two of the elevon-equipped wings and two tail fins. Launch would occur from a rail set at a 45° angle.
The Funryu 4 was 4.0m (13.1ft) long, .6m (1.9ft) in diameter and its span was approximately,8m (2.5ft). Fully loaded its weight was 1,900kg (4,1891b), range 30km (18.6 miles) and ceiling of 15,000m/49,215ft.
Nagasaki Arsenal was tasked with building the Funryu 4 and this did not begin until the late summer of 1945. The first ground test of the missile and its motor commenced on 16 August, but the close of the war prevented the Funryu 4 from being launched or its guidance system fully tested.
To prevent the Allies from learning of the Funryu developments, the UN forbade any of the personnel involved with the Funryu from discussing the project with anyone. In addition, documents, test data, constructed missiles, the launching apparatus and the facilities in which the Funryu was developed were all burned and destroyed.