ROCKET USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING DISTANCE

MAX. BODY DIAMETER

OVERALL LENGTH

GENERAL:

The Mk 172-0 is a VT rocket nose fuze for Navy type fin stabilized rockets designed to function automatically upon approach to the target. It is used only when air burst of the rocket would be most effective to spray exposed personnel in foxholes and light material, with fragments. The complete fin stabilized rocket round is designated 'Rocket Assembly Mk 1 Mod 5'.

DESCRIPTION:

In apperance, the Mk 172 is the same as the VT Ring type bomb fuze T50. The fuze may also be marked as the T2004 for use in Army Rockets. Internally the fuzes are also similar except that a setback feature has been added in the Mk 172-0.

OPERATION:

When rocket launched, the arming wire is withdrawn from the vane locking pin which in turn is forced out by its spring to free the vanes. At the same time, the setback pro-duced by the sudden acceleration forces the hinged inertia weight back against its spring. The hinged inertia weight forces the locking dog from the arming stem gear sec-tor by means of its lever linkage, freeing the gear train. The vanes rotates, driving the electric generator and the gear train. After approximately 100 vane revolutions, the gear sector on the arming stem has rotated 25 degrees clockwise to move clear of the gear train. As the gear sector clears the gear train, the tension spring snaps it 75 de-grees clockwise where it is detained by the stop pin on the hinged inertia weight. Since the arming stem and detonator rotor are integral with the gear sector, they also move 25 degrees by vane rotation and 75 degrees by spring action. The vanes continue to rotate, driving the generator and the gear train which is disconnected from the arming stem. As acceleration ceases at the end of burning of the motor, the spring forces the hinged inertia weight foward, pulling the stop pin and freeing the gear sector. The ten-sion gear snaps the gear sector 90 degrees clockwise into the armed position, lining up the detonator with the booster lead-in and making electrical connection to the firing circuit. The detonator is locked in position by a spring loaded detent in the detonator rotor. When the electric detonator is connected to the firing circuit, the firing conden-ser is charged. After .7 to 1.4 seconds, the condenser has stored up sufficient power and the fuze is armed. On approach to a target, the VT element activates the firing circuit which discharge the condenser through the electric detonator which initiates the explosive train.

REMARKS:

(1) Each fuze Mk 172 Mod 0 is shipped as a complete unit including a seal wire and booster safety pin. It will be recalled that the booster safety pin in this application, like that on the bomb fuzes, gives a visual indication that the detonator rotor is in its origi-nal of safe position, if upon removal of the pin it can be fully reinserted. If it cannot be reinserted, the detonator rotor will have moved out of position and hence, the fuze should be disposed of.

(2) The Mk 172 Mod 0 has neither self-destructive or impact functioning features. However, if the VT fuze is a complete dud the base fuze Mk 157 Mod 0 will cause deto-nation after impact. While the Mk 172 Mod 0 is designed primarily for air to ground firing, it could be used, though less effectively, for air to air firing. In this application the rocket would have to come within 20 feet of the air-craft target in order to func-tion.

(3) A seal wire through a hole in the arming pin inserted at the factory prevents the vanes from rotating and insures that the arming mechanism is in the proper position. Any turning of the vanes, unless accompanied by setback will cause the rotor system to jam, stripping its gears, so that the fuze will be a dud. For this reason, the fuze can-not be pre-armed. If the seal wire is broken when the fuze is originally removed from the container, do not use the fuze. Fuzes in this condition could be disposed of in ac-cordance with security regulations by lowering in deep water or by explosive demolition.

(4) High speed rotation of the vanes is necessary to produce the current to fire the fuze. Therefore, the fuze is actually only armed when in flight on the rocket at speeds in excess of 80 knots. Damged fuzes may hold the electrical charge in the condenser for quits some time. For this reason, damaged fuzes and duds found on the ground should preferably be handled with care. NO DISSEMBLY OF THE Mk 172 Mod 0 IS AU-TORIZED BY FIELD PERSONNEL.