ROCKET USED IN

FUNCTIONING

ARMED CONDITION

ARMING TIME

MAX. BODY DIAMETER

OVERALL LENGTH

COLOR

DESCRIPTION:

These fuzes, identical except that the No. 865 incorporates a delay element where-as the No. 878 is instantaneous, are base detonating fuzes, armed by gas pressure from the rocket motor unit.

The fuze consists of a cylindrical brass housing, closed at one end by a perforated brass plug, and at the other end by a magazine cup containing a booster charge of C.E. Immediately beneath the perforated brass cup is located a metal diaphragm, to which is attached a long arming rod. This arming rod travels through the fuze in a channel drilled off-center through the fuze body. In a central chamber in the fuze body is located a pointed striker and creep spring. In the unarmed position, this striker is held away from the detonator by a retaining ball, which engages an annular groove in the striker and a hole in the fuze body. The ball is held engaged in the striker by the arming rod. Beneath the striker is located a detonator containing about 2 grams of composition "A" or "Al" mixture, a delay pellet of G 20 gunpowder (in the No. 865), a second detonator of lead azide, and a C.E. detonator lead-out. Beneath the lead-out is located a shutter con-taining a booster lead-in of C.E. In the unarmed position, this lead-in is offset, and the explosive channel, however, the stemmed C.E. channel in the shutter is aligned with the rest of the explosive train, forming a direct line to the booster charge in the maga-zine. The shutter is held offset in the unarmed position by the lower part of the arming rod. Two notches are cut in the arming rod, allowing passage to the shutter and clear-ance for the retaining ball when the fuze is armed.

The fuze is armed by the pressure of gases generated by the combustion of gun-powder in the thermal initiator which is used in conjunction with the fuze. The purpose of the fuze is armed. The initiator is positioned in the base of the shell adapter, and when the shell is threaded into the shell ring of the motor, the initiator is brought clo-sely against the front obtruator of the motor. The initiator consists of a thin steel base, adjacent to which is a septum containing LDNR composition (lead dinitro resorcinate). Above the septum is a chamber containing a charge of G 20 gunpowder confined by a cardboard disc, which is held in position by a metal disc with a central hole. The heat from the burning propellant is conducted through the head obturator in the motor and the base of the initiator to the LDNR composition, which is ignited. The LDNR composi-tion in turn initiates the G 20 gunpowder, and the pressure produced reverses the dia-phragm of the fuze and arms the fuze.

OPERATION:

Depression of the diaphragm by the explosion of the thermal initiator moves the arm-ing rod forward until the two notches in the rod are adjacent to the retaining ball and the pin on the lead-in shutter respectively. The shutter is now aligned by its spring with the rest of the explosive train, and the retaining ball is allowed clearance to move out of engagement with the striker.

On impact, the striker rides forward against its spring and strikes the detoantor, which fires the delay pellet (in the No. 865), which in turn fires the secondary detona-tor, lead-out, lead-in, and booster. The explosive train in the No. 878 is identical to that of the No. 865, except that the delay pellet is removed.

REMARKS:

(1) The No. 297 fuze, used in the shells for the 3" LILO assault rocke, is identical to the No. 865 fuze except for the length of the delay time.