Description
This is a chemical long delay nose fuze used in 30, 50, 100, 250 and 500 kg bombs. Its delay time can be 2 - 24 hours. Recommended wait time is 125 hours.
Likely to found with E-1(a) Type 1 antiwithdrawal fuze.
The fuze consists of the fuze body, a nose cap which will not usually be found on a UXB, and a collar which joins the booster to the body. An antiwithdrawal detent prevents the fuze from being unscrewed by hand. An arming spindle is hollowed out to house a copper tank filled with acetone. The arming spindle is held in place by two spring-loaded detents. A screwdriver slot in the top of the spindle allows it to be turned from the safe position ( +) to the armed position ( —) marked in red meaning "firing point." The rotation of the spindle is regulated by the length of the grooves into which the spring-loaded detents are fitted. When in the armed position, the four cut-away segments of the spindle are in line with the raised portions of the inertia weight, thus allowing the latter to move up on impact. The inertia weight is held by two shear wires which are sheared on impact. Two spring-loaded detents hold the inertia weight in position before impact. On impact, the inertia weight moves up toward the top of the fuze, and is locked in this position by these detents. This insures that the firing pin is in line with the primer. When the inertia weight moves up to the armed position, the safety detent remains behind, leaving the firing pin held only by the striker release pin bearing against the soluble plug. When this plug dissolves, the pin moves up, freeing the striker and allowing it to be pushed into the detonator by the spring behind the striker. A rubber sealing ring keeps the solvent from running throughout the fuze after the acetone tank is pierced.
Once the arming spindle is turned through 45° to the firing point, it cannot be turned back to safe. The spring-loaded detents prevent this. Also, after impact, the inertia weight has moved on to the spindle and will prevent rotation.
If the cap is found on a UXB, the fuze may have been armed and the cap may have been replaced.
The antiwithdrawal detent will usually prevent the fuze from being removed from the bomb. If the fuze is removed, the booster and gaine may be set off if the fuze operates later. Therefore, unscrew the booster and gaine immediately after withdrawing the fuze.
Note - Actual time test run by Allied forces on the C-3(a) types A, B, C, and D gave the following average delays:
Type A - 32 minutes.
Type B - 5 hours 3 minutes.
Type C - 12 hours 42 minutes.
Type D - 18 hours 45 minutes.
These tests were run under field conditions which would closely approximate actual dropping of the bomb.
Functioning
Nose cap is removed. The arming spindle is turned to the firing point (—). This turns the spindle so that the inertia weight is free to move ahead on impact. The spindle is locked in position by spring detents. The nose cap may be replaced. On impact, the inertia weight shears the shear wires and moves ahead. The striker is lined up with the primer and is moved away from the stop pin. The acetone tank is pierced and the inertia weight is locked in the armed position by detents. After the acetone has softened the soluble plug, the striker release plunger moves out under spring action releasing the cocked striker which fires the primer.
Hazardous Components
Primer, powder train relay, gaine, and booster.
Physical Data
Length, overall - 7.78 in (197.6 mm)
Length, visible - 1.54 in (39.1 mm)
Width, overall - 3.5 in (88.9 mm)
See Also
Tail, E-1(a), Type 1 Antiwithdrawal
Source(s)
OP 1667, Japanese Explosive Ordnance, Volume 1 (1946)
USNBD - Japanese Bombs & Fuzes (1944)
TM-E9-1984, Enemy Bombs and Fuzes, Section VII, Japanese Fuzes (1942)
