M129 (Impact or Aerial Burst)

Bomb

Functioning

Armed condition

Fuzes used with

Arming time, seconds

Diameter of fuze, inches

Length (with booster), inches

Spindle length, inches

Material

Zinc alloy castings

General: The top section of the fuze is centrally threaded for the arming spindle; the middle section houses the clockwork and firing mechanism; and the base section is a simple flat casting added only to afford a means of screwing the plastic booster cup to the fuze. The fuze screws into the bomb with a left-hand thread, and is thightened with a spanner wrench which fits into the two spanner holes in the top of each fuze. Luting on the threads insures a tight, moisture-resistant fit. Assembly of the fuzes in the bombs is a factory job.

Operation

"Ground" Burst: The release arm is prevented from moving in the unarmed position by the presence of the arming spindle. The release arm is attached to the release rod, which has a cutaway section against which the spring-loaded striker bears. When the arming spindle unthreads about 3.5 turns, the pressure of the striker against the release rod causes it to rotate and move the release arm in a clockwise direction. A gear train through which the external teeth of the release arm pass, controls the speed of the re-lease arm, and in 2.5 seconds the release arm engages the stop arm. Both the stop arm and the release arm are prevented from further rotation by a projection on the impact detent. The fuze is now fully armed. On impact, the impact detent overcomes its light coil spring through inertia, and, as it is forced down, permits both the stop arm and the release arm to be rotated further under influence of the striker spring against the cuta-way release rod. The release rod thus rotates until the striker is no longer retained by the cutaway section, and the striker fires the detonator cap.

"Air" burst: When the setting switch is set for "Air" burst, the fuze operates exactly as above, except that the impact detent has already been depressed by means of the spring-loaded plunger under the setting switch. In this condition, the projection on top of the impact detent does not offer any resistance to the release arm and stop arm during their travel across the face of the mechanism. Hence, the striker is free to fire the deto-nator as soon as the release arm and stop arm have bypassed the impact detent and the release rod has rotated sufficiently to free the striker.

Remarks: This fuze is the only one of the three fuzes for the Bomb M83 which can be identified after it has been inserted in the bomb. Its setting switch, marked "Air-Ground" on top of the fuze, identifies it.

This fuze is a copy of the German (41) butterfly fuze.

In present production, an all-ways action detent replaces the type of detent shown in figure 346.

Figure 346. Impact or Aerial Burst Fuze M129

Figure 347. Details of Fuze M129