Demolition Firing Device Mk 3 (Obsolete)

Length, inches

2.5

Width, inches

Thickness, inches

1.37

General: Essentially, the Demolition Firing Device Mk 3 consists of an ordinary watch movement in which the hour hand is replaced by a cup which is slotted on the outside rim, a release mechanism which carries a bar that rides on the edge of the cup so that the release mechanism will operate as soon as the bar can enter the slot, and a firing pin. The device is waterproof to a depth of 20 feet. Time delay is adjustable up to 11½ hours, with a minimum allowable setting of then minutes. The luminous dial indicates the time remaining before the device fires; the luminous dot on the slotted cup coinciding with the number of remaining hours, and the luminous hand indicates the number of re-maining minutes.

Installation and operation: Unscrew the winding-knob cover and wind the clock in a normal manner. Unscrew the setting knob and set the clock to the desired time, obser-ving the precaution that the clock should never be set for a delay of less than ten minu-tes. Check to see that the bar on the release mechanism is outside the rim of the cup and has not already slipped inside. Check to insure that the clock starter is completely in the "stop" position. Screw the blasting-cap firing device (Special non-electric, 11.01), which has previously been assembled to other articles such as booster, time fuse, demo-lition blocks, primacord, etc., onto the cap chamber. Turn the staring knob to the "start" position. Bend back the protective strip from the safety pin; pull the safety pin out and lock it in place by turning the safety-pin knob counterclockwise as far as possible. The device will then fire when the remaining time has been used up.

Precautions: Time starts running out the instant the clock is started; therefore, do not set the clock for less than ten minutes. Excessive delay in pulling the safety pin after the clock is safety for getting away. Do not attempt to reset the clock without having the safety pin in the "safe" position and without having the starting knob in "stop" posi-tion. Until the device is actually ready for sue, the shipping plug must be kept screwed in place. Premature firing of the device will cause the striker to be thrown out at a speed sufficiently high to cause serious injury to personnel and equipment.

Remarks: The pull ring should be jerked sharply. Once the pull ring has been jerked, there is no way to stop the detonator from exploding.

Figure 254. Demolition Firing Device Mk 3