This is a self-propelled base venturi H.E. rocket stabilized by rotation and fired electri-cally from either the 21 cm Nebelwerfer 42 projector (a two-wheeled field carriage with five barrels) or the 21 cm airborne projector beneath each wing of the Me 109G-6 (Trop) and FW 190. When fired in the former the nose fuze le.Jgr. Z. 23 n.A. or Hbgr.Z. 35 K, are used whilst in the airborne projector the clockwork fuze Zt.Z. S/30 is employed. The complete round weighs approximately 242 lb and its overall length is 49.5 inches. The centre of gravity is 18 inches from the base. The exterior of the rocket is painted deep olive green and stencilled in black. External markings on the round are shown in Fig. 19.

Shell H.E.B.C. filled amatol 40/60;

Nose fuze le.Jgr.Z. 23 n.A., Hbgr.Z. 35 K, or Zt.Z. S/30;

Gaine Zdlg. 36 Np;

Tail tube with propellant charge and ignition system;

Venturi block with grid;

Electric ignition fuze.

Fig. 19

The general shape of the shell is a truncated ogive of high crh. form the base. The filled shell, including the fuze weighs approximately 98 lb. The bursting charge, indicated by the numeral "13" stencilled on the body, is amatol 40/60 and weighs approximately 22.4 lb. The shell body is of steel with a solid base; it is screwthreaded externally at the base for the attachment of the tail tube and, on the shoulder to receive the ballistic cap. The overall length of the shell including the threaded portions, is 15.8 inches. The diameters at the base and shoulder are 8.38 inches and 5.3 inches. The shoulder is screwthreaded internally to receive an adapter, which in turn takes the fuze and a steel exploder con-tainer. A steel distance piece 1.5 inches long and 1.54 inches in diameter, with a central flash hole 0.32 inch in diameter, separates the fuze from the gaine. A cork washer at-tached to the end of the distance piece is in contact with the fuze.

The ballistic cap, approximately 8.5 inches long, is of thin metal and shaped to the ge-neral contour of the shell body. The nose is flat and bored centrally to receive a screwed adapter supporting the upper end of a wooden rod. The wooden rod rests on the top of the fuze and forms an extension to the striker. It is retained by spinning the nose of the adapter over a flat retaining disc. The base of the cap is screwthreaded internally for at-tachment to the shell body.

Fig. 20

The fuzes le.Jgr.Z. 23 n.A. and Hbgr.Z. 35 K, and the gaine Zdgl. 36 Np are described as separate items in this pamphlet. Fuse Zt.Z. S/30 is described in Pamphlet No. 8, page 11.

The tail unit has an overall length of 27.2 inches and weighs approximately 144 1/4 lb fil-led. The main parts comprise a steel tail tube, steel venturi block, propellant charge, steel grid and an ignition system.

The tail tube weighing 87 lb. 2 oz. is cylindrical in shape, 26.6 inches long and 8.27 in-ches in diameter, except at the venturi end and near the head end, where the diameters are slightly increased. The wall is machined inside and out to a thickness of 0.394 inch. The head end is closed by a diaphragm formed in the tube. A cavity approximately 1.25 inches deep in front of the diaphragm is screwthreaded internally to receive the base end of the projectile. The opposite face of the diaphragm is recessed to the shape of a sau-cer approximately 7 inches in diameter across the rim. The centre of this recess has a cavity partially to accommodate the forward igniter. Internally, the venturi end is screw-threaded to receive the venturi block.

The venturi block is solid, flanged and screwthreaded externally for insertion in the end of the tube. Twenty-two venturis, equally spaced on a circle 6.08 inches in diameter, have their axis inclined at an angle of 16 degrees to the axis of the rocket, so that the escaping gases cause the round to rotate in flight. An axial venturi in the centre of the block extends into a boss formed on the front face. The boss is screwthreaded externally to take a grid supporting the base end of the propellant charge. The venturis have the throat diameter of 0.362 inch and open at an inclusive angle of 26 degrees.

The propellant charge, weighing approximately 39 lb. 9 1/4 oz., consists of six sticks of tubular propellant surrounding a seventh. Each is 21.66 inches long, 2.45 inches and 0.32 inch external and internal diameters respectively. The forward end of the outer sticks is held by a shoulder formed in the tube near the rim of the saucer-shaped recess; the centre stick is held by the lugs of the igniter holder. A preliminary chemical analysis shows that charge is basically approximately 59 per cent nitrocellulose and 37 per cent diglycoldinitrate.

The grid supporting the charge at the venturi end is shaped to form three concentric circles on a web of six radial arms; it weighs 1 lb. 10 oz., and its overall diameter is 7.3 inches. The centre circle is screwthreaded internally to enable this grid to be screwed to the boss on the front face of the venturi block. The arms are chamfered on the base side towards their outer ends.

The ignition system comprises a forward igniter, a length of primed celluloid tubing and a rear igniter.

The forward igniter, which weighs 3 ozs., is housed within a steel split ring, forming an igniter holder with six lugs bent inwards to form distances pieces. The igniter consists of a pellet of pressed grey powder composed of aluminium and barium nitrate under a thin black layer of compressed zirconium metal and potassium nitrate. Across the face of this thin layer is a perforated strip of nitrocellulose. The filling is contained in a flat circular aluminium container 2.57 inches in diameter, and retained by turning over the lip of the container on to a ring of compressed paper.

The rear igniter, accommodate immediately in front of the venturis and in rear of the grid, is in the form of a celluloid "U" section ring filled gunpowder. The external and inter-nal diameters of the ring are 6.78 inches and 5.6 inches respectively, and its outer and inner thickness 0.5 and 0.33 inches respectively.

The celluloid tubing is 22.35 inches long and is accommodated in the central stick of pro-pellant. It contains quickmatch and at each end a perforated gunpowder pellet. The for-ward pellet is accommodated centrally whithin the lugs of the igniter holder. The rear pellet protrudes slightly from the base of the central stick.

The outer venturis are closed by a thin ring of aluminium foil, 6.76 inches in diameter, fit-ted against the front face of the venturi block. The centre venturi is closed by a thin disc of aluminium foil 1.96 inches in diameter fitting in the cavity in the front face of the grid.

Fig. 21

This is an electric ignition fuze and is described elsewhere in this pamphelt. It is pushed into one of the venturis when the rocket is loaded into the projector for firing.

An electric current fires the ignition fuze and the flash ignites the rear igniter, which in turn ignites the length of quickmatch in the celluloid tube and the forward igniter. The latter ensures complete ignition of the propellant charge. Pressure set up inside the tube and escaping through the ventruis propels the rocket forward. The inclined venturis cause the rocket to rotate and stabilize it in flight.

On impact, the ballistic cap is shattered and the wooden rod is driven in to fire the fuze. The flash from the fuze passes through a flash channel in the steel distance piece to de-tonate the gaine which in turn detonates the shell filling.