AN-M103A1 (Nose Mechanical Impact)

General: The Nose Mechanical Impact FUze AN-M103 is being replaced by the AN-M103A1, which differs in that the striker block has been drilled and tapped to accommo-date an arming screw of a greater diameter. The hole for the arming screw joins that of the arming stem. In this way, it is possible for the collar on the arming stem, under pres-sure of the arming-stem spring, to bear against the base of the widened arming screw. In the earlier production of the AN-M103A1, a threaded sleeve was fitted and staked to the original arming screw of the AN-M103 to form the new widened arming screw. In the later productions, the widened arming screw is a single solid piece. In other respects, the AN-M103 and AN-M103A1 are similar.

The purpose of modifying the Nose Mechanical Impact Fuze AN-M103 as described above is to eliminate the possibility of accidental detonation in crash landings, and thus make it safe for carrier usage. In some cases, during crash landings, upon initial impact, the vane cup and head of the AN-M103 were sheared off, allowing the arming stem to jump out, and the slider to align itself below the firing pin. Ob subsequent nose impact, the fuze fired. The AN-M103A1 increases the safety primarily because the arming stem cannot jump out on accidental shearing of the vane cup assembly, as the arming screw overlaps the arming-stem collar.

Operation: The operation of the AN-M103A1 is the same as that of the AN-M103 ex-cept that, in the former, the arming stem, in addition to bearing against the internal gear, has its collar bearing against the arming screw. As the arming screw moves out, the arming stem follows it until the arming-stem collar bears against the setting pin for delay action, or against the top of the cavity for instantaneous action. In a crash land-ing, if the vane cup and head of the fuze shear off, the arming stem is held in place by the arming screw; hence, the slider cannot move over and the fuze will not fire.

Remarks: Air travel to arm the AN-M103A1 is the same as the AN-M103, since the AN-M103 has 28 double threads per inch on the arming screw while the AN-M103A1 has 14 single threads per inch.

Figure 325. Nose Fuze AN-M103A1