Rocket Fuzes

Rocket Fuzes

Rocket fuzes are primarily classified by their location in the warhead; for example, nose fuze or base fuze. They are further classified by mode of operation, such as impact-firing, mechanical-time, acceleration and deceleration, or proximity. All fuzes contain safety/arming devices to prevent detonation during normal transporting, handling, and launching of the complete rocket.

A representative fuze from each class is discussed in the following paragraphs. The fuzes currently in use and their primary application are listed below. For more detailed information on fuzes, refer to Aircraft Rocket Systems 2.75-inch and 5.0-inch NAVAIR 11-75A-92.

IMPACT FIRING FUZES.—Impact firing fuzes (fig. 2-12) function when the rocket strikes a target that offers sufficient resistance to cause crushing or other disarrangement of actuating parts. All current impact firing rocket fuzes have the same type of safety/arming mechanism. This mechanism consists of an unbalanced rotor, which, under setback forces, drives a gear-train timing system. A given minimum acceleration over a given length of time is required to complete the arming cycle. If rocket acceleration is too low or extends over too short a period of time, the arming mechanism returns to the unarmed condition. The timing mechanism provides a safe separation distance from the launcher before arming. When located in the nose of the warhead, impact firing fuzes are known as point-detonating (PD) fuzes. If they are located in the base of th warhead, they are known as base-detonating (BD) fuzes. Nose and base fuzes function either instantaneously or after a short delay that gives the warhead time to penetrate the target before functioning.

MECHANICAL TIME FUZES.—Mechanical time fuzes (fig. 2-13) function by the action of a mechanical timer. These fuzes contain a safety/arming device and a clock mechanism. The arming mechanism is similar to those in impact detonating fuzes and requires a minimum acceleration over a given time to complete the arming cycle. Upon arming, the mechanical timer is started, and after a set elapsed time, the fuze initiates the firing train. The Mk 193 Mod 0 is the only mechanical time rocket fuze currently in use. It is permanently installed in the nose of the Mk 33 Mod 1 flare warhead.

ACCELERATION-DECELERATION FUZES.— Acceleration-deceleration fuzes are similar to impact and time fuzes because they require acceleration for a given time to complete the arming cycle. After the arming cycle is completed and the rocket velocity begins to drop, deceleration causes the fuze to function. The Model 113A is the only accelerationdeceleration fuze in use by the Navy at this time. It is a base-mounted fuze that is permanently installed in the WDU-4A/A flechette warhead.

PROXIMITY FUZES.—Proximity fuzes, sometimes referred to as VT fuzes (fig. 2-14), initiate by "sensing," usually by electronic means, the presence and distance of a target. Proximity fuzes are primarily used in air-to-ground operations where air bursts above the target are desired. They are not suitable for use against targets that require penetration and detonation within the target for effective destruction. In general, proximity fuzes consist of an electronics package in the forward end, a thermal battery, a safety/arming device, and an explosive booster in the base. The arming mechanism is similar to those in impact detonating fuzes, and it requires a minimum acceleration over a given time to complete the arming cycle.

NOTE: Some rocket fuzes designed for use with 2.75-inch warheads can be used with the 5.0-inch warhead by using the BBU-15/B adapter booster (fig. 2-15).