20 cm Rocket Projectile and Launcher

Japanese 20 cm Rocket Projectile and Launcher

This ground-launched rocket is fired from a trough shaped launcher approximately 7 feet long, which weighs approximately 175 pounds. The Japanese claim a range of 1,800 meters (1,970 yds.) at 50° elevation. The rocket is spin-stabilized, rotating in a clockwise direction. The complete round, without fuze, is approximately 41 inches long and weighs 198.3 pounds.

The projectile has a straight body and an ogival nose. It is fitted with a centrifugally armed point detonating fuze. In addition to this standard fuze, the Type 91 Time, Type 100 Combination, and Type 88 P.D. fuzes will also fit the fuze pocket. However, it is not known whether the rocket will produce sufficient setback to arm these fuzes. The explosive charge, Type 91 (trinitroanisol), is cast directly into the lacquered interior of the case. The base plate which screws into the projectile body is also threaded to take the motor.

The motor body, a straight cylinder, is closed at the rear by a base plate to which a grid is attached. A perforated cup fits against the motor closing plate at the forward end. Seven sticks of propellant (nitroglycerine, nitrocellulose, NaCl, and centralite) fit securely into the combustion chamber between the perforated cup and the grid. Six sticks form a circle around an identical central stick; all have only a single axial perforation.

The motor base plate of hardened steel has six offset nozzles and a central threaded opening for a percussion type primer. Ignition is mechanical and from the forward end. A black silk powder bag lashed to the perforated cup forms the ignition charge.


Weight of projectile without fuze         49.9 kg.–110 lbs.
Weight of high explosive filling 17.5 kg.–38.6 lbs.
Overall length of projectile without fuze 588.0 mm–23.14 ins.
Minimum diameter of orifices 15.0 mm–.591 ins.
Angular cant of nozzles 25°
Diameter of body 210.5 mm (approx. 8.30 ins.)
Wall thickness 12.0 mm–.472 in.
Overall length of motor body 460 mm–18.11 ins.
Weight with propellant 40.0 kg.–88 lbs.
Weight of propellant 8.3 kg.–18.3 lbs.
Weight of black powder ignition charge 50.6 grams–1.77 ozs.
Wall thickness 10.0 mm–.39 in.
Length of propellant sticks 290.0 mm–11.41 ins.
Diameter of propellant sticks 58.0 mm–2.28 ins.
Diameter of perforation 11.0 mm–.43 in.
Weight of propellant sticks (each–varies slightly) 1.162 kg.–2.56 lbs.

Japanese: p. 352 (April 1, 1945)

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