ROCKET USED IN

Mk 157-2

Mk 159-1

Mk 161-0

Mk 163-0

Mk 164-0

Mk 165-0

FUNCTIONING

Mk 157-2, Mk 163-0

Mk 165-0

Mk 159-1, Mk 164-0

Mk 161

Instantaneous impact

Mk 157-2; Mk 159-1:

In order to secure a more adequate sealing for the protection of the explosive in the 11.75" and 5.0" rocket heads from the hot gases during the burning of the motor, the base fuze were modified in that a projectile type gas check was added around the fuze body ahead of the threads. The fuzes are shipped assembled in the base of the head. The lead washer, with copper hood is pressed into place at the loading activity and is not to be disturbed in the field.

The Mk 157-2 is the Mk 157-1 fuze (see page 101) with the projectile type gas seal; the Mk 159-1 is the Mk 159-0 fuze (see page 101) with a projectile type gas seal. These fuzes will be replaced by the Mk 163-0 and the Mk 164-0 respectively.

MK 161-0:

The Mk 161-0 was developed from the Mk 146-1 (see page 99) to secure better sealing of the motor gases from the high explosive filling of the head and to eliminate the possible firing of an unfuzed round. The Mk 161-0 will replace the Mk 146-1 in the 7.2" Demolition Rocket (Mk 10 head).

Mk 163-0; Mk 164-0:

The Mk 163-0 is similar to the Mk 157-2 and the Mk 164-0 is similar to the Mk 159-1. In addition to retaining the projectile type gas seal noted above, the Mk 163-0 and Mk 164-0 fuzes have an improved detonator shutter locking arrangement. Formerly, the shutter was retained in the safe position in the safe position by a projection which locked in a recess of the body during setback, and was held in that position by the force of acceleration during the bruning of the motor. This allowed the detonator up-ward movement as well as rotation which contributed to their malfunctioning.

The new design has removed the projection and replaced it with a shutter lock pin which is mounted in a setback block. The block is retained in position by a setback block spring. As the rocket is launched, the force of setback moves the block back to compress the setback block spring. The lock pin moves up to contact the detent to move upward and compress the detent spring. As the motor burns, the firing pin is withdrawn from the shutter to leave only the lock pin to prevent the shutter from pivo-ting. As the motor burns out and deceleration sets in, the setback block spring and the detent spring force the setback block forward, thereby withdrawing the lock pin from the shutter. This frees the detonator shutter and the spring acts to pivot the shutter over in the cavity and align the firing train.

The Mk 163-0 will replace the Mk 157-2 in the 11.75" Mk 1-1 and Mk 2 heads; the Mk 164-0 will replace the Mk 159-1 in the 5.0" Mk 6-1 head.

Mk 165:

The Mk 165-0 differs from the Mk 157-0 only in that the head of the fuze has been modified to receive the motor and the booster is approximately .3 inch longer to incor-porate the improved detonator shutter locking arrangement described in the preceding section.

The adapter in the fuze head is threaded to receive the 3.25" Mk 7 motor and the Mk 165-0 will replace the old motor adapter in the base of the 5.0" Mk 1 head as well as the Mk 157-0 fuze.