Mk 157 Mod 2, Mk 159 Mod 1, Mk 161, Mk 163, Mk 164, and Mk 165

Rockets uses in

Mk 157 Mod 2

Mk 159 Mod 1

Mk 161 Mod 0

Mk 163 Mod 0

Mk 164 Mod 0

Mk 165 Mod 0

Functioning

Mk 157 Mod 2, Mk 163 Mod 0,
Mk 165 Mod 0

Mk 159, Mod 1, Mk 164 Mod 0

Mk 161 Mod 0

Non-delay

Mk 157 Mod 2 and Mk 159 Mod 1: In order to secure a more adequate sealing for the projection of the explosive in the 11.75-inch and 5.0-inch 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 fields.

The Base Fuze Mk 157 Mod 2 is the Base Fuze Mk 157 Mod 1 with the projectile-type gas seal; the Base Fuze Mk 159 Mod 1 is the Mk 159 Mod 0 with a projectile type gas seal. These fuzes will be replaced by the Base Fuze Mk 163 Mod 0 and Mk 164 Mod 0 respectively.

Mk 161 Mod 0: This fuze was developed from the Mk 146 Mod 1 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 Base Fuze Mk 161 Mod 0 will replace the Mk 146 Mod 1 in the 7.2-inch Demolition Rocket Head Mk 10.

The Mk 161 Mod 0 differs from the Mk 146 Mod 1 only in that the head of the fuze has been modified to receive the motor. The 7.2-inch Head Mk 10 Mod 1 has been silght-ly altered to accommodate the new motor adapter. The 3.25-inch motor will thread into the fuze, and a threaded reducer is supplied to permit use of the 2.25-inch motor.

Mk 163 Mod 0 and Mk 164 Mod 0: The Base Fuze Mk 163 Mod 0 is similar to the Mk 157 Mod 2, and the Mk 164 Mod 0 is similar to the Mk 159 Mod 1. In addition to retaining the projectile-type gas seal previously mentioned, the Base Fuze Mk 163 Mod 0 and Mk 164 Mod 0 have an improved detonator-shutter locking arrangement. Formerly, the shut-ter was retained in the safe position by projection which locked in a recess of the body during set-back, and was held in that position by the force of acceleration during the burning of the motor. This allowed the detonator upward movement as well as rotation, which contributed to the malfunctioning of the earlier fuzes.

The new design has removed the projection and replaced it with a shutter lock pin which is mounted in a set-back block. The block is retained in a set-back block. The block is retained in position by a set-back block spring. As the rocket is launched, the force of set-back moves the block back to compress the set-back 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 pivoting. As the motor burns out and deceleration sets in, the set-back block spring and the detent spring force the set-back block forward, thereby withdrawing the lock pin from the shutter. This free the detonator shutter, and the spring acts to pivot the shutter over in the cavitiy and align the firing train.

Mk 163 Mod 1: This fuze differs from the Mod 0 in that the diameter of the inlet ori-fice has been decreased and the diameter of the shear wire increased, to increase the arming pressure to 350 pounds per square inch.

The Base Fuze Mk 163 Mod 0 will replace the Mk 157 Mod 2 in the 11.75-inch Heads Mk 1 Mod 1 and Mk 2; the Base Fuze Mk 164 Mod 0 will replace the Mk 159 Mod 1 in the 5.0-inch Head Mk 6 Mod 1.

Mk 165 Mod 0: This fuze differs from the Base Fuze Mk 157 Mod 0 only in that the head of the fuze has been modified to receive the motor and the booster is approximate-ly 0.3 inches longer, to incorporate the improved detonator-shutter locking arrangement descirbed under the Base Fuze Mk 163 Mod 0 and Mk 164 Mod 0.

The adapter in the fuze head is threaded to receive the 3.25-inch Motor Mk 7, and the Base Fuze Mk 165 Mod 0 will replace the old motor adapter in the base of the 5-inch Head Mk 1, as well as the Fuze Mk 157 Mod 0.

Figure 164. Gas Check for Navy Fuzes Mk 157 Mod 2, Mk 159 Mod 1,
Mk 163 and Mk 164

Figure 165. Motor Adapter in Fuzes Mk 161 and Mk 165

Figure 166. Modified Detonator Shutter Lock for Fuzes Mk 163, Mk 164,
and Mk 165