Mk 137 Mods 0-2 and Mk 145 Mods 0 and 1

Rocket uses in

Functioning

Arming time

Vane guard diameter, inches

Over-all length (without booster), inches

2½

General: These fuzes fire upon water impact for velocities of 300 ft./sec. and more, and at impact angles as small as 15° to 20°. They probably will not arm if the burning time is shorter than 0.2 second, or the velocity is less than 300 ft./sec.

Operation: When the rocket is loaded on the launcher, the safety pin securing the set-back collar is withdrawn. On firing the rocket, the set-back collar is forced back by inertia, compressing the set-back spring and withdrawing the vane locking pin from the hole in the vane boss. The vanes rotate freely, and after three to four rotations have unthreaded the striker spindle sufficiently that, when deceleraton occurs, the vane lock-ing pin cannot again engage the vane boss. After about ten vane rotations, the striker spindle is unthreaded sufficiently to free the detonator shutter, which is forced across the shutter cavity by its spring. It is stopped by the stop pin and is locked in the armed position by a spring-loaded detent housed in the shutter, which slips into a recess in the striker guide. When the striker has reached the end of its threads, it rotates freely with the vanes as the striker spindle collar rides in a groove in the underside of the fuze body. On impact, the threads on the fuze body are sheared as the striker is forced into the de-tonator.

The Mk 137 Mod 1 resembles the Mk 137, but has then blades on the arming vanes as compared to eight, and also has a split spacer sleeve.

The Mk 137 Mod 2 is similar to the Mk 154 Mod 3. A modified vane lock-pin seat pre-vents premature arming.

The Mk 145 is similar to the Mk 137 but incorporates a 0.02-second delay in the deto-nator.

The Mk 145 Mod 1 has a modified vane lock-pin seat preventing premature arming.

Figure 151. Navy Nose Fuze (Rocket) Mk 137 Type