DESCRIPTION. The fuze consists of two main parts, the upper part which has a liquid-tight closed inner end is very similar to the upper portion of the (17) A fuze and serves a similar purpose (heat from a thermite charge, via an aluminum cylinder, arms the lower part of the fuze). The switch on the fuze head is a dummy, as also is one of the plun-gers. One specimen has been recovered with no switch on the fuze head.

The lower section of the fuze consists a polystyrene molding, which houses a simple wi-ring circuit, which connects two 1.5-volts dry cells with a low tension electric igniter. The circuit is connected in parallel with four sensitive switches. Three of these are of the mercury type, while the fourth is a normaly vibratory switch. Two of the mercury switches are in the horizontal plane, at right angles to each other. The third mercury switch and the vibratory switch are in the vertical plane, parallel to the longitudinal axis of the fuze.

In the hinge of a collet which receives the aluminum incendiary boss from the upper sec-tion of the fuze is a fusible metal plug, which anchors one end of a spring under tension. This spring, while so anchored, acts as a safety device by short-circuiting the electric igniter. A secondary safety-device is contained in the flange of the collet, where a poly-styrene pellet is positioned to prevent a spring-loaded electric contact plunger from arm-ing the firing circuit. (See fig. 186A and 186B.)

A gaine is screwed into the base of the fuze, and the flash channel of the gaine contains a pressed powder relay pellet.

The base of the fuze is conical in shape, and around the base runs a split steel ring. When the fuze is withdrawn, the ring rides up the slope of the cone and jams against the side of the fuze pocket, preventing withdrawal of the fuze.

Figure 186A – 50b or "Y" Electrical Antidisturbance

OPERATION. On impact the thermite composition held in the container in the upper sec-tion of the fuze is ignited by the flash from the igniter bridge. This incendiary composition heats the walls of the aluminum boss of the fuze body which melts both the polystyrene pellet contained in the flange of the collet and the fusible metal plug contained in the hinge of the collet.

Under the influence of its spring, the contact plunger moves forward to arm the firing cir-cuit. Under its own tension, the metal spring is drawn clear to the fused metal plug and ceases to short circuit the igniter bridge. The fuze is now fully armed.

The fuze now operates as a normal (50) fuze so fas as the vibratory switch is concer-ned, while a rotation of 2° is sufficient to close one or more of the mercury switches. These four switches are wired in parallel, and the closing of any one will immediately complete the firing circuit and fire the igniter bridge. The flash from the low tension igni-ter bridge ignites the relay pellet in the gaine holder, and the flash from this pellet initia-tes the explosive gaine and detonates the bomb.

REMARKS. 1. Construction type 4A. 2. It is reported that this fuze can remain active for several months.

Figure 186B – 50b or "Y" Electrical Antidisturbance Wiring Diagram