M131 (Anti-Disturbance)

Bomb

Armed condition

Fuzes used with

Arming time

Diameter, inches

Length, inches

Spindle length, inches

Material

Two zinc castings

General: The fuze consists of two castings, the top one having a center hole threa-ded for the arming spindle and the outer threads to screw the fuze into the bomb; the lower casting containing the timing, anti-disturbance, and firing mechanisms, with its base internally threaded for the tetryl booster cup. The assembly is held together by three long screws. On one side of the lower casting is a large hollow screw which holds the firing pin and the firing-pin spring under compression. Diametrically opposite is anot-her smaller screw retaining the primer detonator.

Operation: When the arming spindle has been withdrawn approximately 0.25-inch, the escape-wheel spring and the timing gear are freed, and the fuze commences to arm. During the complete operational circle, the fuze acts in three successive steps, as fol-lows:

1. After about 0.5 second, during which time the timing gear rotates in a clockwise direction under the influence of the coiled drive spring, the entire mechanism is brought to a halt as the stud on the impact spring engages the stud under the timing gear; and the fuze remains in this condition until impact.

2. On impact, the force of inertia on the flat impact spring is sufficient to disengage the studs on the impact spring and the timing gear. The timing gear now continues its rotation fpr a period of approximately five seconds, until the stud, seated in place above the timing gear, engages a small projection on the end of the anti-disturbance block. Here the timing gear is once again brought to a halt, with the fuze in a fully armed posi-tion. The fuze is now in an extremely sensitive condition, since the anti-disturbance block is supported only by the delicate anti-disturbance-block spring.

3. Should the fuze now be subjected to handling, shock, or vibration, the projection on the anti-disturbance block and the stud above the timing gear would become disen-gaged. The timing gear can thus make its firnal run, this time until its blank segment per-mits it to slip by the small gear (with which it was previously engaged) with increased momentum. During this last swift movement, the stud under the timing gear strikes the release-arm stop, moving it away from the release arm, and the spring-loaded striker can now rotate the release-arm cam as the release arm is freed. The cam is forecd around in a clockwise direction, permitting the striker to slip by and fire the detonator cap, intiat-ing the booster.

Remarks: There are no markings on the fuze to identify it; and, when fitted into the bomb, it cannot be distinguished from the Fuze M130. This fuze is so sensitive that the vibration caused by an aircraft propeller near by may be sufficient to release the anti-disturbance block and fire the fuze.

This fuze is copied from the German (70) B, butterfly fuze.

Figure 349. Anti-Disturbance Fuze M131