The Japanese recognised the value of the artillery rocket to then under armed forces and carried out considerable design and development work in order to provide a weapon that could make up for their lack of industrial capacity. Unfortunately for them their results were patchy and well behind the work carried out by the Allies. To add to the lack of Japanese success there were often development programmes carried out in opposition to each other, and typical of these were the projects to develop a 20-cm (7.87in) rocket by both the army and the navy. The Army 20-cm Rocket may be regarded as the better of the two projects. It was a spin-stabilized rocket using six base vents to Impart propulsion and spin, and had an overall resemblance to an artillery projectile. To fire this rocket the army provided what appeared to be an oversize mortar known as the Type 4 Rocket Launcher. The rocket was inserted into the 'barrel' by raising part of the upper section of the barrel and part of the tube base was open. This launcher was supposed to deliver the rocket relatively accurately, but few types of these appeared to have been issued and most of them that were, was used for coastal defences. The Navy 20-cm Rocket resembled the army weapon in many respects, but was intended for launching from troughs made from simple wooden planks or in some cases more sophisticated metal troughs. At times the rockets were simply emplaced to be launched directly from holes dug in the ground A more conventional launcher used in small numbers only was a simple barrel on a light artillery-type carriage. These 20-cm (7.87-in) rockets formed the bulk of the Japanese rocket programmes but there were others. One was the Type 10 Rocket Motor which was a simple propulsion unit designed to push aircraft bombs along ramps or troughs to launch them At least two versions of the Type to existed but they were very inaccurate and had a maximum range of only 1830 m (2,000 yards). The launchers used for these rocket motors were often improvised, and improvisation was also used In at least one case where the conventional fins of an aircraft 250-kg (551-lb) bomb were replaced by a large rocket motor for launching from a simple wooden trough. Some Intelligence reports from the period (1945) speak of these launchers mounted on trucks, but no confirmation of these has been found. The largest of all the Japanese rockets had a diameter of 447 mm (17.6 in), and this 44.7-cm Rocket was a somewhat crude spin-stabilised design that was used in action on Iwo Jima and Luzon. It had a range of 1958 m (2,140 yards) at best, and was launched from short wooden racks or frames. It was Wildly Inaccurate, but it did have a warhead weighing 180.7 kg (398lb) By the time these rockets were used Japanese industrial capacity was in such a state that the conventional high explosive warheads for these rockets often had to be replaced by simple picric acid. Japan undertook considerable development work on rockets, but lagged behind the other belligerent nations and produced few usable weapons. This 20-cm army rocket was one of the small number to see action. Specification Army 20-cm Rocket Dimensions: length 984 mm (3875 in) Diameter: 202 mm (795 in) Weights: overall 92. 6 kg (44.95Ib) Propellant not known; filling 16.2 kg (35.7Ib) Performance: initial velocity not known; range not known Specification Navy 20-cm Rocket Dimensions: length 1.041 m (41 in) Diameter: 210 mm (8.27 in) Weights: overall 90. 12 kg (l98.5Ib) Propellant: 8.3 kg (18.3Ib); filling 17.52 kg (386Ib) Performance: initial velocity not known; range 1800 m (1, 970 yards)
The maximum range of this 20 cm Rocket was about 2,400 m or 2600yd. But the service life of this gun was too short, just from 1943 to 1945.
