Mk 229 and AN-Mk 230 (Tail Hydrostatic) (Obsolete)

Bombs

Mk 229

AN-Mk 230

Functioning

Armed condition

Fuzes used with

Arming time

Over-all length, inches

Body diameter, inches

Vane span, inches

Material

Steel, aluminum alloy, and brass

General: These two fuzes are identical, except that the part of the Tail Hydrostatic Fuze Mk 229 fitting into the bomb body is 1.3 inches longer than the corresponding part of the AN-Mk 230; hence, the AN-Mk 230 cannot be used in bombs that take the Fuze Mk 229. The AN-Mk 230 fits into the Adapter Booster M115 or M115A1, and can be used in the general-purpose bombs taking that adapter booster for use against marine targets.

Operation: The desired depth setting is accomplished by turning the depth-setting knob and thereby compressing the depth spring the proper amount. If a functioning at 125 feet is desired, the spring would be compressed the maximum amount, consequently causing the water pressure to overcome the greater resistance of more tightly coiled springs. If a shallow-water functioning is desired, the springs would be only partially compressed, and the water pressure necessary to overcome the more loosely coiled springs would be considerably less. In setting, the depth-adjusting sleeve is raised to the desired spring compression by means of a five-sided cam secured to the external depth-setting knob, and resting under a projection of the depth-adjusting sleeve.

On release from the plane, the arming wire is withdrawn and the vanes are free to ro-tate. This rotation is transmitted by the vane shaft through a series of reduction gears to the arming shaft. The upper gear has one more tooth than the lower gear, and, as the pinion gear rotates around the lower stationary gear, the upper gear is pushed around clockwise one tooth per revolution of the vanes. This rotation of the upper gear causes the arming screw to rotate clockwise, since the upper gear and arming screw are positi-vely secured; and, because of the right-handed threads on the screw, the detent retai-ning cup threads up on it. As the cup clears the two arming detents locking the depth-spring stem nut, their springs force the detents out, freeing the depth spring stem and the piston. The fuze is then armed. On impact with the water, the inertia counterbalan-ces prevent the firing assembly from moving down and prematurely firing the fuze becau-se of the deceleration caused by impact. As the bomb submerges, water enters two ports in the outer body and through holes in the depth-setting mechanism housing. Hy-drostatic pressure, acting on the sylphon bellows, forces the hydrostatic piston down-ward, compressing the firing spring, until the retaining balls fall out into the widened por-tion of the piston. The firing plunger is then forced downward by the pressure of the compressed firing spring onto the fixed firing pin, setting off the explosive train.

Remarks: The detonator consists of fulminate of mercury and tetryl pellets. The booster lead-in, relay pellets, and booster are tetryl.

The O-ring gasket has replaced the Garlock gasket. In using the O-ring gasket, a sup-port ring (steel washer 0.120 inch thick) must be used to assure metal contact between the fuze and fuze-seat liner, thereby preventing distortion of the fuze on impact.

Do not disassemble this fuze without reinserting the safety pin through the lower fuze body and firing plunger.