This is a self-propelled base venting rocket, stabilized in flight by rotation caused by the inclined venturis. The rocket is fired electrically from the 30 cm Nebelwerfer 42. The complete round weighs approximately 277 lb. Its overall length is 46.5 inches; the maxi-mum diameter of the bomb is 11.75 inches and of the tail tube 8.56 inches. The centre of grafity is 21.75 inches from the base. The exterior of the rocket is painted deep olive green and the stencilling in black, except the abbreviated nomenclature of the round "30 cm WK Spr." near the nose end, which is stencilled in white. External markings on the round are shown in Fig. 22.

Shell H.E. filled amatol 40/60;

Nose fuze;

Gaine;

Tail unit with propellant charge and ignition system;

Primer electric C/23 with contact unit.

The weight of the filled shell without fuze and gaine is approximately 147 lb. The general shape of the shell is an ogival head of medium crh., whilst the remainder of the body is streamlined towards the base. The body consists of two wall sections and a solid nose and base welded together circumferentially. The wall sections are appoximately 0.1 inch thick and welded at their maximum diameter. A rib is formed in the body behind the weld. The rear section is also welded longitudinally. The nose section is screwthreaded inter-nally to receive a nose fuze and a steel exploder container. In transport the nose is clo-sed by a plastic plug. The base is screwthreaded internally for the attachment of the tail tube.

The bursting charge as indicated by the numeral "13" stencilled on the body, is amatol 40/60.

Fig. 22

The tail unit has an overall length of 22.6 inches and weighs approximately 129 lb 10 oz filled. It consists essentially of the tail tube, venturi block, propellant charge, two grids, and an ignition system with electric primer and spring contact.

The steel tail tube is cylindrical in shape, 8.34 inches in diameter except near the base, where humped band is formed to increase the diameter to 8.56 inches. The wall of the tube is 0.43 inch thick and machined both externally and internally. The head end is clo-sed and screwthreaded externally for insertion into the shell. Internally, at the base end, it is screwthreaded and provided with a shoulder to receive the venturi block.

The solid venturi block is flanged and screwthreaded externally for insertion in the venturi end of the tube. Eighteen venturi holes are drilled in the block with their centres on a circle of 3.05 inches radius. The throat diameter of each venturi is approximately 0.82 inch. The axis of the venturi are inclined at an angle of 12 degrees 42 seconds, so that the effluent gases cause the round to rotate in flight. A thin tin plate ring fits into a circular recess in the base of the block and seals the venturi exits. The base of the block is stamped thus: "Wu 18 x 9,3 Ø 12° 42asw 5a" indicating the number, the throat diame-ter in millimeters, and the inclination angle of the venturis. The centre of the venturi block is bored and screwthreaded to receive an adapter. To facilitate assembly in the tail tube, two key recesses are provided in the base of the block.

The propellant charge weighs 33 lb. and consists of six tubular sticks of propellant sur-rounding a seventh. Each is 18.4 inches long, 2.45 inches and 0.32 inch external and in-ternal diameters respectively. Preliminary chemical analysis has shown that the charge contains 59.9 per cent nitrocellulose and 35.4 per cent diglycoldinitrate.

The cast steel grid supporting the venturi end of the charge is shaped to form four con-centric circles on a web of six arms. The webs are chamfered on their base side towards their outer ends. The grid is bolted to the venturi block by the primer adapter.

The grid at the forward end of the charge consists of a split ring with eight pairs of lugs and a sheet of metal mesh. Each pair of lugs is bent inwardly to a "U" shape in section, and the metal mesh is welded to two adjacent lugs diametrically opposite the split. In addition to spacing, the grid prevents the igniter being crushed by the charge.

The ignition system consists of an igniter, a primed celluloid tube and an electric primer unit.

The igniter, which weighs 3 oz., is housed within the split ring and held centrally opposite the central stick of propellant by an igniter holder. The igniter consists of a pellet of pressed black powder with a perforated N.C. powder pellet in strip form acorss its sur-face. The pellets are contained in a flat aluminium capsule and retained by turning over the lip of the capsule on to a compressed paper ring. The igniter holder is a plate of sheet steel, 0.04 inch thick, 3.95 inches wide and 7.42 inches long, radiused at the ends to suit the curvature of the grid split ring. A hole 2.6 inches in diameter is bored in the centre of the holder, and a ring-shaped in section, to hold the igniter, fits into the hole and is spot werded at six points.

The celluloid tube, accommodated in the central stick of propellant, is 19.7 inches long and 0.23 inch and 0.0394 inch external and internal diameters. It contains quickmatch and at each end a perforated gunpowder pellet. The forward pellet is accommodated centrally within the forward grid and is in contact with the igniter. The pellet at the other end is accommodate in the vent of the primer adapter.

The primer adapter, which also bolts the rear grid to the venturi block, is screwthreaded externally and flanged at one end; it is inserted into the venturi block from the front, and two flats formed on the periphery of the flange enable it to be screwed home with the aid of the spanner. The adapter is bored centrally in four dimensions with a coned vent at the flanged end. Two chambers formed in the base end of the boring are screwthrea-ded to receive the electric primer and contact unit respectively, and the others form a necked flash channel which houses the gunpowder pellet and the rear end of the inflam-mable tube. The smaller of the threaded borings, formed in the centre of the adapter, re-ceived the electric primer "C/23" described as a separate item in this pamphlet. The lar-ger boring nearer the base houses the spring contact unit. The unit consists of a plastic insulating bush, steel pin, steel spring and brass cover cap. The bush is cup-shaped with a central hole bored in its base; it is screwthreaded externally for insertion in the adapter and internally to receive the cover cap. The contact pin is a stem with circular flat head and is inserted inside the bush so that the stem portion protrudes the hole to make con-tact with the contact plug of the electric primer. The pin is kept in contact by the spring held in compression between the head of the pin and cover cap. The cover cap is cup-shaped to house the spring and head of the pin, and screwthreaded externally for insert-ion in the bush.

Fig. 23

An electric current passes through the contact unit and fires the primer. The flash from the primer ignites the gunpowder pellet and quickmatch in the celluloid tube, which in turn ignites the igniter, bringing about ignition of the propellant. Pressure set up in the tail blows off the thin metal ring closing the venturi exits, propels the projectile, which, owening to the inclination of the venturi, is rotated.