Mk 27 Mods 0 and 1

Projectiles used in

Over-all length, inches

Diameter, inches

Threaded length, inches

Threads

Weights, grams

Material

Arming speed, r.p.m.

Description: Internally, the fuze consists of two major housings: the firing pin hous-ing and the rotor housing. Within the firing pin housing is a metal firing pin held in place by two firing pin detents which are surrounded by a circular copper band acting as a de-tent spring. Above the firing pin housing is a plastic firing pin extension which serves as a safety feature in the event that the fuze is dropped in the unarmed condition. The rotor housing consists of a rotor, with lead counterweights and detonator assembled in a rotor block. The axis of the detonator is inserted at an angle of about 55 degrees to the axis of the fuze. The line of center of the lead counterweights, being perpendicular to the axis of the detonator, is at an angle of about 35 degrees to the axis of the fuze. The ro-tor is held in this unarmed position by the two rotor detents, the tapered ends of which engage in the holes in the side of the rotor. In this position the detantor is not in line with the firing pin or booster.

Operation: This fuze is armed entirely by centrifugal force which accomplishes three things:

1. The firing pin detents are moved outward against the copper band, thus freeing the firing pin. The copper band is arranged so that the ends of it overlap, allowing room for expansion.

2. The rotor detents are moved back against their spring, freein the rotor.

3. The lead counterweights are caused to turn the rotor until they are at a maximum radius from the axis of rotation of the fuze. In this position, the detonator is aligned with the firing pin and booster. The rotor is held in this position by centrifugal force.

On impact, the nose of the fuze is crushed and the firing pin extension pushes the fi-ring pin into the detonator.

Remarks: The Point Detonating Fuze Mk 27 Mod 1 differs from the Mod 0 in that the firing pin detents are of a different shape and are known as "hour-glass" detents. On set-back, the firing pin will move back against the detents, and, because of their shape, they will be held in place until the firing pin moves forward again under the influence of creep.

The fuzes will function on duralumin sheet but not on water impact.

The plastic firing pin extension is designed as a safety device in the event of acciden-tal dropping. If the round is dropped, the plastic extension will shatter, whereas a one-piece metal firing pin might force its way past the firing pin detents and initiate the fuze.

Figure 83. Point Detonating Fuze Mk 27 Mod 0