DATA:

BOMBS USED IN

M111A2

M127

M138

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

VANE SPAN

MAX. BODY DIAMETER

OVERALL LENGTH

MATERIAL

GENERAL:

The M127 fuze is found by assembling the booster and detonator assembly from an AN-M110A1 fuze to a M111A2 fuze body. The result is a mechanical time fuze with an 18 grain tetryl booster instead of a black powder booster such as in the M111A2. The M138 fuze is the same as the M127 except that the M138 has only 7 grain of tetryl, the balance of the space being taken up by an inert clay pellet. (M127 booster was too powerful for E6R2 cluster adapter and damaged the bombs in the cluster, hence reduc-tion of tetryl).

OPERATION:

The desired time interval is set on the graduated scale and the locking screw tight-ened. Upon release of the cluster or Flare from the plane, the arming wire is withdrawn from the fuze, the vanes are free to rotate and the arming pin jumps out.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 stationary gear rotate on the ball race, the idler gear is rotated, thus rotat-ing 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 has one more tooth than the stationary gear, it lags one tooth on every rotation and gradually unscrews downward. After approximately 250 vane revolutions, the arm-ing sleeve has unthreaded far enough to be withdrawn from the safety block, which is then thrown clear by centrifugal force.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 arming-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 that 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 relea-sed and impinged 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 by any obstruction between it and the primer.

EARLY DESIGNS:

Original M111 had setting range of from 15-93 sec., and because of greater number of teeth on gears required 570 vane revolutions to arm.

M111A1 reduced minimum setting time on the scale from 15 to 5 seconds, however oculd not be set for less than 8 seconds, since if set for less, the clockwork functioned before the fuze was armed, and the firing pin spring pulled the striker down tightly against the safety blocks stopping the rotation of the vanes, thus preventing aerial burst. Both of these early designs had three 120° section safety blocks with a groove which received the arming sleeve of the movable gear. They also had weaker gears with more teeth and larger, weaker vanes.

REMARKS:

M111A2 booster contains 70 grains of black powder.

Neither the M127 or the M138 should be assembled to their respective clusters, until the cluster has been locked in place the bomb rack.

The M127 is being replaced by the M128; the M138 is being replaced by the M145; the M111A2 is being replaced by the M146. (See page 183)

These fuzes are equipped with a spinner device (See page 182) to force the safety block to rotate with the arming vane and insure positive ejection of the safety block after the arming sleeve has withdrawn. (Only later lots of M111A2 are equipped with spinner device).

In order to insure correct rotation of the arming vane of the M111A2 when used in the M26 cluster, the fuze has been modified by replacing the standard vane by an ane-mometer type vane. When so altered, the fuze will be known as the T77. This change will be made in the field with kits supplied by the Army.