Tag Archive for '20cm'

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)

20 cm K. (E): Railway Gun


Batteries of these railway guns in concrete emplacements were found on both the Cherbourg and Brest Peninsulas in France. Equipment consisted of the gun, carriage, turntable, power plant and electrical operating unit, and ammunition car.

The piece is of the built-up type, consisting of a tube and two jackets. It is screwed into the breech ring. The breechblock is of the horizontal sliding wedge type. The hydropneumatic recoil system has two cylinders located under the carriage; the pistons are fastened to the lower end of the breech ring.

The carriage, when mounted on a turntable, has a traverse of 360 degrees; it is estimated that elevation is from 0 to 840 mils.The turntable, consisting of two sections bolted together, rotates on a central pivot and a portable circular track. Four wheels at each end of the turntable support it on the track. Electric motors are geared through these wheels to rotate the piece in azimuth. It is very similar to the 28 cm K. 5 (E) reported on page 100.2.

A small ammunition car, equipped with a removable roof, is mounted on trucks and runs on a two-rail track which is built in as a part of the turntable track.


Weight of gun       45,500 lbs.
Weight of carriage w/ gun 189,000 lbs.
Caliber 203 mm (7.982 ins.)
Weight (firing position) 92.5 tons
Length (traveling position) 63 ft. (approx.)
Height (traveling position) 13 ft.
Height (firing position)
Width (overall) 13 ft. (approx.)
Track Std. railway gage 56 1/2 ins.
Length of tube 30 ft., 7 ins.
Length of tube and breech 32 ft., 8 1/2 ins.
Length of rifling 22 ft.
Rifling Uniform R.H. twist
No. of grooves 64
Width of grooves 0.188 in. (approx.)
Depth of grooves .125 in. (approx.)
Width of lands
Muzzle velocity (shell) 2,800 f/s
Range (est.) 36,000 yds.
Traverse (on turntable) 360°
Elevation (estimated) 47°
Length of recoil (from recoil index slide) 25 1/2 ins.
Ammunition APCBC, APBC, HE, Practice, Illuminating with parachute
Wt. of projectile 259 lbs.
Wt. of propellant (max. charge) 96.5 lbs.

German: p. 102.1 (May 1, 1945)