Construction: Excepting the set-back plunger and gaine, this fuze is constructed en-tirely of brass and made of two pieces. The base of the rear portion contains an oblong slot into which the rear end of the threaded spindle and/or striker is fitted. On the threads of the striker rides an inertia weight which is free to revolve about the striker except for a set-back plunger which, in the unarmed position, rests partially in a recess in the inertia weight and partially in a stationary collar in the fuze body, thus preventing any revolution of the inertia weight. This inertia weight prevents the striker from falling onto the primer of the gaine. The forward end of the striker fits down through an inner collar, which is a part of the forward section of the fuze. Immediately before the threa-ded portion of the striker is a split collar which is wedges between the threads and the inner collar, affording an additional safety feature.

Operation: On set-back, the flanged inertia plunger moves back into the recess of the inertia weight. Since the striker is keyed to the fuze and thus spins with the fuze, the inertia weight lags behind and moves back to the base of the fuze. The force of impact causes the striker to move forward, overcoming the split brass collar, onto the primer.

Figure 449 – Type 3rd-year Mk 1 Base Impact Fuze.