M81, M48A2, or M51

Rocket uses in

Functioning

Over-all length, inches

Weight, pounds

Threads

14 N.S.-1

General: The Fuze M81 consists of the Artillery Fuze M48A2 assembled with either the Booster M21A1 or the Booster M24. Depending on where the fuze is assembled, it may be marked M81, M48A2, or M51. Only the 0.05-second delay models of the M48A2 fuzes are loaded in rockets at present.

Description: Much like the Navy's Fuze Mk 29 or Mk 30 in construction, this fuze adds a delay firing train. The choise of instantaneous (super-quick) or delay firing is made on the selector sleeve of the interrupter device - the slot being set parallel to the longitu-dinal axis of the fuze, or within 15 degrees either side, for super-quick action, and at right angles thereto for delay action.

The interruptor sleeve is thicker on one side than on the other. When set for "Delay", the thick side holds the interruptor in the flash channel, blocking any flash through that tube. When the sleeve is set for "Super-quick", the thin side of the sleeve allows the in-terruptor to move up into the sleeve by centrifugal stimulus, clearing the flash channel.

The instantaneous action is like that described for the Mk 29. The delay firing train is a separate unit in the base of the fuze. There are two plunger pins or centrifugal detents holding the delay assembly in the unarmed position. When the fuze is armed, there is a firing pin positioned over a primer, which leads to a black-powder delay, and, in turn to a flash pellet.

Operation: No action takes place upon firing until sufficient rotational speed has been established to overcome the resistance of springs and set-back force on the several safety devices. When the fuze is set for super-quick action, after it leaves the muzzle, centrifugal force causes the interruptor to move outward, opening the passage. At the same time, the plunger pins locking the delay assembly in the unarmed position also mo-ves outward, releasing that assembly in preparation for impact. The plunger-pin lock then swings on its pivot under centrifugal force, placing an arm against the inner end of each plunger pin, preventing the return of the pins to the unarmed position. Upon impact, the firing pin of the super-quick action is driven against the detonator, initiating the super-quick action. Inertia causes the delay-action plunger to move forward, driving the primer against the delay-action firing pin and initiating the delay action. In normal functioning with super-quick action, the delay action has no effect, since the super-quick train will have caused the rocket to explode before the delay train can burn for its prescribed time. However, should the super-quick action fail, the fuze will function with delay action rather than

Figure 141. Army Nose Fuze (Rocket) M48A2