(Fig. 40 and 41)

This bomb, an invention of Commandatore Manzolini, is also known as the "Thermos" bomb because of its resemblance in appearance to a thermos flask. It is an H.E. bomb fitted with a fuze which becomes fully armed after impact and sub-sequently initiates the detonation of the bomb when disturbed by handling etc.

The body of the bomb is constructed of 3/8 inch seamless mild steel tube 2½ inches in diameter and 7 inches long, prepared at the tail end to receive the fuze and closed at the other end by a steel disc which is welded in position. The bursting charge consists of approximately 2 lb. T.N.T. The body is painted brown and the overall length (with fuze) is 14 inches.

Fig. 40

The fuze consists of a striker spring (1) held under compression between two cup-sha-ped containers, one fitting over each end of the spring. The cup fitted over the tail end of the spring (2) carries a piston and is prevented from rising by three balls (3), located in the walls of the liquid cylinder (4), which bear on a shoulder formed on the cup. The cup fitted over the other end of the striker spring (5) carries the striker and is prevented from moving out of the liquid cylinder by three pairs of steel balls (6) also located in the wall of the liquid cylinder and bearing on a shoulder formed on the cup.

The liquid cylinder is of brass and is closed at the tail end by a screwed plug (7). A cir-cumferential flange (8) is formed externally about its centre to limit its downward move-ment within the front cup. Above and also below this flange the cylinder is prepared to house two sets of three steel balls. The upper set prevents the piston cup from rising and the three balls are retained in position by an inertia sleeve (10). The three steel balls below the flange (11) are retained by the piston cup and the open end of the front cup (12). While these balls are in this position further movement of the liquid cylinder into the front cup is prevented. Near the front end the liquid cylinder has a circumferential groove (13) which in combination with a screw carried in the front cup limits the axial movement of the cylinder. Below this groove the cylinder is prepared to house three pairs of steel balls which support the striker cup. At the front end the cylinder is recessed to acco-mmodate a weak spiral spring (14). Internally the cylinder is designed to form an oil chamber for the piston and a circumferential flange is formed to position the piston and striker cups.

The front cup, which receives the forward end of the liquid cylinder, is of brass and car-ries a small detonator (15) positioned over a flashhole leading ot the larger detonator (16) which is carried in the body of the fuze and is in contact with the bursting charge. The cup has an internal circumferential groove (17) to receive the steel balls supporting the striker cap when the fuze is fired.

The tail cup (18) which fits over the tail end of the liquid cylinder is of brass and enclo-ses a strong spiral spring (19) held under compression between the tail end of the liquid cylinder and the closing plug of the tail cup (20).

The body of the fuze (21) is screw-threaded for insertion in the bomb and is fitted with a hollow steel cylinder (22) within which the liquid cylinder assembled with its front and tail cups, etc., is held by means of two loose tubular positioning pieces, one above the tail cup (23) and the other below the front cup (24). Three holes are provided in the wall of this body cylinder, near its centre, to receive the claws (25), fitted to spring strips to support the inertia sleeve of the liquid cylinder. The body cylinder is closed at the tail end by a brass screwed plug which is prepared to receive the screw-threaded shaft of the arming vanes and is flanged to support one end of the arming spring (26). The arming sleeve (27) is a short blackended cylinder with rubber insert which fits over the body cy-linder and is positioned between the arming spring and the claws with three distance pie-ces (28). The distance pieces and the three spring strips carrying the claws are retained in the engaged position by an aluminum tail cap (29) which is secured over the tail of the fuze by the arming vanes. Projecting louvrelike fins (30) are formed in the end of the tail cap.

Fig. 41

The arming vanes are of aluminium, one of the vanes being prepared to receive a safety pin which, when in position, prevents rotation of the vanes.

Before release the safety pin is removed from the arming vanes, thus allowing the vanes to be rotated by air resistance during the descent to the bomb. The rotation of the arm-ing vanes unscrews the shaft of the vanes from the brass cap of the body cylinder and releases the aluminium tail cap, which is then removed from the fuze by the spring strips carrying the claws and the action of the air against the fins of the tail cap. The removal of the tail cap permits the claw spring strips and the distance pieces to fall away and the arming sleeve is moved by its spring to seal the claw holes in the body cylinder. This movement of the arming sleeve assists in the withdrawal of the claws and the removal of the tail cap. The with-drawal of the claws removes the support between the inertia ring and the external flange on the liquid cylinder and leaves the ring supported by a small projecting ring formed on the cylinder.

On impact the tail cap sets down over the liquid cylinder, compressing its spring and driving the inertia ring down on to the external flange of the liquid cylinder. This move-ment brings the groove on the inside of the inertia sleeve in line with the steel balls in the wall of the liquid cylinder which retain the piston cup of the spring. These balls enter the groove and allow the piston to rise under the force of the spring and against the resistance offered by the oil flowing through the clearance between the piston and the cylinder wall. The upward movement of the piston removes the support of the piston cup from the steel balls located in the wall of the liquid cylinder below the flange and permits the balls to enter the cylinder, thus removing the means of preventing the liquid cylinder from further entry into the front cup. This further entry is now opposed by the weak spi-ral spring below the liquid cylinder and the fuze is fully armed.

On being subjected to a sudden movement or jarring action the opposition of the spring is overcomes by the movement of the liquid cylinder into the front cup or that of the front cup over the liquid cylinder, according to the direction from which the disturbing force is applied. Either of these movements brings the groove inside the front cup in line with the three pairs of steel balls located near the front end of the liquid cylinder which support the striker cup. The balls enter the groove and the striker is driven by its spring on to the initiating detonator and the detonation of the bursting charge is brought about throught the main detonator with which is its in contact.

From the drawing avaible the fuze appears to be designed to function also on the "al-ways" principle when the disturbing force is applied laterally. In these circumstances a sudden movement or jarring action would cause the liquid cylinder to reach the firing po-sition within the front cup as the result of the closing movement of both of these com-ponents. The movement of the liquid cylinder would be brought about by the convex sur-face of the closing plug of the tail cup moving down the concave underside of the clos-ing plug of the body cylinder and transmitting the movement to the liquid cylinder through the intervening spring. Cor-responding movement of the front cup, in the oppo-site, would be brought about by the incline on the front end of the front cup moving down the corresponding incline in the fuze body. In each case the inclined sides of the grooves accommodating the tubular positioning piece appear to facilitate these move-ments.

The sensitivity of the fuze is dependent on the strength of the spiral spring in the front cup. The existence of a green bomb of this type fitted with a more sensitive fuze has been reported.