M144 (Nose Clockwork Aerial Burst)

Bombs

Functioning

Armed condition

Fuzes used with

Arming time

Vane span, inches

Body diameter, inches

Over-all lenght, inches

Material

Aluminum alloy body with zinc- or cadmium-plated steel striker

General: The Nose Clockwork Aerial Burst Fuze M144 is similar to the AN-M146, ex-cept that it has direct-drive instead of gear-reduction arming, resulting in ejection of the safety block after approximately six to none turns of the arming vane. The direct drive involves the removal of the stationary gear from the arming hub, the movable gear from the arming sleeve, and the idler gear from the pin. The arming-sleeve stop plate fixed to the bottom of the arming sleeve has a fork which engages the pinion-gear pin and pre-vents the arming sleev from rotating. This change was made to ensure that the safety block is ejected in less than the mechanical functioning time of the fuze. In addition, the M144 incorporates a clock mechanism which runs three times as fast as the AN-M146 clock mechanism. This results in a minimum setting of 1.6 seconds instead of 5, a maxi-mum setting of 30.6 seconds instead of 92, and a slider arming time of 1.5 ± 0.5 seconds instead of 4.5 ± 1.5. Because of the shorter running time, the clockwork is more accu-rate in the M144.

Operation: Upon release of the bomb, the arming wire is withdrawn from the fuze; the vanes are free to rotate; and the arming pin jumps out. The vanes are positively at-tached to the arming hub and rotate as one unit. The arming sleeve, which is threaded to the arming hub, is preventing from rotating, since the stop plate attached to it enga-ges the idler-gear pin. However, the arming sleeve moves down as a result of rotation of the arming hub; and after approximately six to nine vane revolutions the arming sleeve has withdrawn far enough for the safety collar to be thrown clear by centrifugal force. The timing disc, meanwhile, has been rotated by the spring-driven clockwork. After 1.5 ± 0.5 seconds of rotation, the timing disc cam, located below the timing disc (and turning with it), frees the crank-shaped end of the arming stem. The rest of the operation is the same as for the M146.

Figure 339. Aerial Burst Fuze M144