USNBD, Bombs and Fuzes; Section III - Bomb Fuzes: AN-M128, AN-M145, AN-M146, AN-M147

U.S.N.B.D. - UNITED STATES - BOMBS AND FUZES; PYROTECHNICS

SECTION III - BOMB FUZES

DATA:		U.S. ARMY NOSE FUZES
		AN-M128, AN-M145 AN-M146, AN-M147
BOMBS USED IN
AN-M128	Cluster Aimable Incendiary
	AN-M17A1
AN-M145	Cluster Adapter, Aimable	(Service)
	Incendiary E6R2
AN-M146	Flares and photoflash, and	CLOCKWORK AERIAL FUZE
	butterfly bomb cluster M28
	and M29, M89, 90, 98 T.I.B
AN-M147	M84 Target Identification
	bomb; AN-M47A2, A3
	Incend.
FUNCTIONING	Aerial Burst, 5-92 sec.;
	or impact instantaneous if
	slider aligned.
ARMED CONDITION	When safety collar and arming pin are both out, and detonator
	is aligned under firing pin.
FUZES USED WITH	None for M128, M146 and M147; M152 or M153 used with M145.
ARMING TIME	Approximately 260 vane revolutions.
VANE SPAN	3 in.
MAX. BODY DIAMETER	1.93 in.
OVERALL LENGTH	AN-M128, AN-M145 - 6.2 in.; AN-M146 - 5.67 in.; AN-M147 - 5.72 in.
MATERIAL	Aluminum alloy body with zinc or cadmium plated steel striker.

GENERAL:

These fuzes modified the M111A2 by the addition of a detonator slider held out of line until the fuze is partially armed by a crank-shaped arming stem. The four fuzes in the series are identical except for the boosters employed; the AN-M128 has the boos-ter of the M127 (tetryl); the AN-M145 uses that of the M138 (tetrly-clay pellets); the AN-M146 employs that of the M111A2 (black powder); and the AN-M147 uses the AN-M126A1 primer detonator instead of a booster.

OPERATION:

The desired time interval is set on the graduated scale and the locking screw; tigth-ened. Upon release of the cluster from the plane, the arming wire is withdrawn from the fuze, the vanes are free to rotate and the arming pin jumps out.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 arming vane, nut, outer ball race, arming hub and stationary gear rotate as a unit. As the vanes and sta-tionary gear rotate on the ball race, the idler gear is rotated, thus rotating the movable gear and the arming sleeve to which it is attached. The arming sleeve is threaded into the arming hub and extends inside the safety block. Since the movable gear hase one more tooth than the stationary gear, it lags one tooth on every rotation and gradually unscrews downward. After approximately 260 vanes revolutions, the arming sleeve has underthreaded far enough to be withdrawn from the safety block, which is then thrown clear by centrifugal force.

The timing disc, meanwhile, has been rotated by the spring driven clockwork. After approximately four seconds of rotation, the release arm located below the timing disc (and turning with it), frees the crank-shaped end of the arming stem. The lower end of the arming stem then presents its cut-away section to the detonator slider which will then align itself below the firing pin and become locked in place there by a spring load-ed detent.

When the detonator is aligned, the timing disc continues to turn. After the predeter-mined 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. This in turn frees the half round cocking pin which is forced to rotate under pressure of the spring loaded firing pin. As the half round cocking pin rotates, the firing pin is released and impinges on the primer, firing the booster.

REMARKS:

The AN-M129 replaces the M127; AN-M145 replaces the M138; AN-M146 replaces the M111A2.

These fuzes are equipped with a spinner device (see opposite page) to force the safety block to rotate with the arming vane - this assures positive ejection of the safe-ty block after the arming sleeve has withdrawn.