DATA:

BOMBS USED IN

Mk 237 Mod 0

Mk 238 Mod 0

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

VANES SPAN

MAX. BODY DIAMETER

OVERALL LENGTH

MATERIAL

Zinc or cadmium plated steel.

GENERAL:

These fuzes differ only in the length of their arming stem. Delay arming is obtained by means of the 30 to 1 gear reduction system which is like that of the M115 series tail fuze. Upon completion of arming, the gear reduction assembly and the arming stem do not separate from the fuze, but cease rotation. Functioning time of these fuzes is de-termined by a lead shear wire (50% lead, 50% tin). The various delays are obtained by varying the diameter of the wire, i.e., increasing the diameter for longer delays. The slider carries a Mk 23 detonator which is made up of three explosive components; namely, azide priming mixture, lead azide, and tetryl. The fuze incorporates a tetryl booster lead-in, but does not have an integral booster.

OPERATION:

The complete arming of the fuze is effected in two stages: air travel and impact. Upon withdrawal of the arming wire the vane assembly rotates, causing the arming stem to rotate via the gear reduction system. The lower end of the arming stem is en-cased by the firing pin housing nut which in turn is pinned to the firing pin housing. To the bottom of the firing pin housing is attached the slider stop. In addition, the firing pin is locked to the firing pin hosuing by two balls and the firing pin housing in turn is locked to the ball retainer sleeve by two balls. As the arming stem screws upward the entire firing assembly moves upward under the action of the ball retainer spring. After approximately 150 revolutions of the vanes, the firing assembly has risen sufficiently to withdrawn the slider stop and firing pin from the slider slot, allowing the slider to align its detonator below the firing pin. (A detent locks slider in position). Continued rotation of the vanes causes the "O" Ring Gasket on the firing pin housing nut to seat and stop rotation of the vane assembly.

On impact the ball retainer sleeve is forced down by the inertia freeing the retaining balls. At the instant deceleration ceases, the ball retainer sleeve is forced upward by its spring, allowing the firing balls to jump out ot their recess, and the spring loaded striker is restrained only by the lead shear wire. The fuze is now fully armed. The firing pin under action of its spring exerts pressure on the lead shear wire and causes the wire to shear when the proper length of time has elapsed, depending on temperature conditions. The firing pin strikes the detonator, which in turn sets off the booster lead-in.

REMARKS:

(1) These fuzes incorporate an anti-withdrawal feature, but no booby trap device like the M123 series. Under normal handling and installation, the anti-withdrawal feature does not function, since the locking ball and its carrier are held in place in the deep part of the eccentric groove, by a carrier pin and spring. Upon impact, however, the force of inertia is sufficient to withdraw the carrier pin from the fuze body, and allow the carrier spring to pull the ball carrier into the shallow part of the eccentric, locking the fuze in place. The fuze body is case hardened to prevent removal with a wrench after impact. Since these fuzes require impact to lock in place, bombs with these fuzes can be safely returned to the base or carrier, and fuzes removed for stowage.

(2) Since these fuzes have a 2" thread diameter, it is necessary to remove the inner sleeve of the M115A1 adapter booster before installation. Fuzes should be screwed securely into adapter booster, otherwise dud may result. A special short length locking pin is shipped with these fuzes for securing the M115A1 adapter booster to the base plug.

(3) Bombs fuzed with these fuzes should not be released at an altitude lower than that specified by CominCh as the minimum safe altitude of release for instantaneous action fuzes, for if the bomb is subjected to multiple impact, the first impact would completely arm the fuze, and the second might shear the lead shear wire allwowing the fuze to fire without delay.

(4) These fuzes are detonator safe. In the unarmed position, the detonator is lined up with the safety expansion chamber. If the detonator should function prematurely, the force of detonation is dissipated in this cavity, and will not set off the booster lead-in charge, or adapter booster charge.