12-cm ordinary projectiles (semifixed).

12-cm ordinary projectiles (fixed).

12-cm incendiary-shrapnel projectiles (fixed).

12.7-cm ordinary projectiles (fixed).

12.7-cm incendiary-shrapnel (fixed).

14-cm illuminating projectiles (bag).

15-cm illuminating projectiles (bag).

15.5-cm illuminating projectiles (bag).

Construction: Type 91, the fuze body consists of an aluminum nose cap, and a nickel- plated brass time-setting ring, locking ring, and base section. Housed in the nose cap is a spring-supported set-back hammer. Immediately below the set-back hammer is a spring-driven clock mechanism identical in construction to those in Japanese bomb fuzes D-2 (a), D-2 (b) and D-2 (c). However, this fuze is started by set-back and maintained in the armed position by centrifugal force. The time-setting firng has a vertical opening on its top rim by which the clock may be wound with an appropriate tool after the nose cap has been removed. There are two exterior setting lugs. One is secured to the time ring and the other to the lower portion of the fuze body. The time-setting ring is gradua-ted in one-second intervals from 0 to 55 seconds.

Operation: Before firing the gun, the setting disk is connected to the time setting ring of the fuze by the control arm. It is not connected to the clockwork, but is free to ro-tate around the clockwork spindle when the time-setting ring of the fuze is moved in the setting. Setting of the fuze varies the distance the setting disk must be rotated by the clockwork before the striker release arm will fall the slot in the setting disk and release the striker.

Until the gun is fired, the clockwork is held immobile by the escapement release arm con-nected to a vertical shaft. A torsion spring working on the shaft tends to rotate the es-capement release arm away from the clockwork gears. It is prevented from doing this by a projection on the upper end of the vertical shaft which bears against a shoulder of the clock-starting plunger.

Figure 443 – Type 91 Mechanical Time Fuze.

When the gun is fired, the set-back hammer is left behind with sufficient force to:

1. Bend the control arm out to engagement with the time setting ring.

2. Drive the clutch bar down into a slot in the upper end of the clock – thus spreading it sufficiently to clutch the setting disk to the clockwork spindle. At the same time, the clock-starting plunger is left behind by setback and thereby removes the shoulder from in front of the extension of the escapement release-arm shaft, allowing the escapement re-lease arm to be rotated free of the clockwork gears. The clockwork is now free to run and starts to rotate the setting disk in a counterclockwise direction. With centrifugal for-ce, a centrifugal safety lock is thrown out from below a shoulder of the striker, which is now free to be released.

When the clock-starting plunger moves downward, its upper end is removed from the ou-ter end of the striker release arm, which is now free to move outward under the impulse of the striker release arm spring, and its inner end then bears against the setting disk. When the setting disk is rotated sufficiently to bring the notch into alignment with the inner end of the striker release arm, the striker release arm spring forces the outer end of the release arm out, thereby pivoting the inner end into the slot of the setting disk. When this happens, the striker release arm moves out of its notch in the striker, which is then driven downward onto the primer cap, initiating the detonation of the projectile via the medium of the auxilary fuze.

Figure 444 – Type 91 Mechanical Time Fuze.

Remarks: There is a modified version of this fuze that has a gear ring for automatic set-ting. This is used in the 12.7-cm ammunition for the 12.7-cm A.A. gun which has an au-tomatic time-setting device.