DATA:

BOMBS USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

VANE SPAN

MAX. BODY DIAMETER

OVERALL LENGTH

MATERIAL

Aluminum alloy body with zinc or cadmium plated steel striker.

GENERAL:

The M155 (formerly the T71) is the same as the M111A2 except that the gear re-duction system has been eliminated. A spinner device is incorporated to force the safe-ty block to rotate with the arming vane. Elimination of the gear reduction system has been accomplished by removing the stationary gear from the arming hub, and pinning the pinion gear in place so that it cannot rotate.

OPERATION:

Upon release the cluster from the plane, the arming wire is withdrawn from the fuze, the vanes are free to rotate and the arming pin jumps out. The vanes are positively attached to the arming hub and rotate as one unit. The arming sleeve, which is thread-ed to the arming hub, is prevented from rotating since the movable gear which is attached to it, meshes with the pinned pinnion gear. However, the arming sleeve moves down due to rotation of the arming hub, and after approximately 6-9 vane revolutions the arming sleeve has withdrawn far enough for the safety block to be thrown clear by centrifugal force. The timing disc, meanwhile, has been rotated by the spring-driven clockwork. After the predetermined time has elapsed, the slot in the timing disc will be positioned opposite the timing disc lever. Through a series of levers, pressure forces this timing disc lever into the slot thus freeing the firing lever. Since the half round pin is no longer retained by the firing lever, it is free to rotate under the pressure of the spring-loaded firing pin, a collar on the firing pin bearing on one side of the notch in the half round pin. As the half round pin rotates, the firing pin is released and impinges on the primer, firing the booster.

If the timing mechanism should fail, the fuze would still detonate on impact, because the striker would be forced down and would shear any obstruction between it and the primer.

REMARKS:

The M155 replaces the M111A2 in the above-mentioned clusters. Replacement was made since clusters fuzed with the M111A2 sometime failed to open with low fuze set-tings since the cluster flight is not always stable enough to permit arming of the M111A2 fuze before the set time expires. Elimination of the gear reduction system obvi-ates this difficulty. The spinner insures ejection of the safety block at completion of arming.

This fuze is not procured by the Navy.