DATA:

BOMBS USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

VANE SPAN

MAX. BODY DIAMETER

OVERALL LENGTH

MATERIAL

Cadmium plated steel with some brass parts

GENERAL:

The AN-M103 is the standard nose fuze in service. When shipped the fuze is set for delay action. One auxiliary booster is required when this fuze is used in Navy bombs. When used in light case, frag., chem., and incendiary bombs and aicraft depth bombs, the fuze should be set for instantaneous action to prevent breaking up of the bomb case before detonation occurs.

OPERATION:

When bomb is dropped, arming wire is pulled and vanes rotate. The two pinion gears are rotated counter-clockwise, their off-center hubs walking the external-tooth gear backwards around the teeth of the internal-tooth gear, which is thus cranked in a counter-clockwise direction. The outboard edge of the internal-tooth gear is grooved and rides screws projecting through from the vane cup, maintaining an even position. The arming screw, being positively attached to the base of the internal-tooth gear, is gradually unthreaded from the striker. As it unthreads it lifts the entire vane assembly, including the vane cup. After 220 revolutions of the vanes, the vane cup will clear the safety discs. which spring free, leaving the striker secured only by the shear wire and setting pin. The spring-loaded arming stem will rise as the vane assembly rises, being retained only by the base of the internal tooth gear. If the setting is for delay action, however, the setting pin will be depressed into the deep slot and will protrude into the channel of the arming stem to engage the collar on the arming stem after it has risen only sufficiently to clear the step in the detonator slider, lining the detonator up with the delay firing train. On impact the force of inertia will cause the striker body to shear the shear pin and setting pin and the delay firing pin will impinge on the delay primer, setting off the flash which ignites the delay pellet, relay, primer, detonator, booster lead-in, and booster is succesion. The instantaneous firing pin will merely protrude into the empty channel positioned to receive it. If set for instantaneous action, the setting pin will be in the shallow slot and will not protrude into the arming stem channel. After an additional 110 revolutions of the vane (330 total), the vane cup will have been lifted high enough to have the arming stem moved out of the slider cavity, allowing the slider to line the primer detonator beneath the instantaneous firing pin. The slider is motiva-ted by two springs and is locked in the armed position by a spring loaded detent. On impact the firing pin will impinge directly on the primer, setting off the detonator, boos-ter lead-in, and booster in succesion. Even though an instantaneous setting is used, the delay striker will impinge on the delay primer, setting off the delay pellet. It is thus possible that the fuze would function on delay, even though set for instantaneous act-ion, if it failed to function instantaneously.

EARLY DESIGN:

The M103 fuze had 32 single threads per inch on the arming screw instead of 28 double threads per inch on the AN-M103, resulting in an arming time of 850 vanes re-volutions for instantaneous firing and 525 vane revolutuions when set for delay action. The M103 had a larger and weaker vane construction.

REMARKS:

(1) Especially large vanes have been designed for the AN-M103 for use with flat no-sed depth bombs, as the regular vanes have difficulty in amring.

(2) The AN-M103 can be used for dive bombing, but not for masthead bombing.