Color: Natural brass or fuze with steel body may be yellow due to coat of laquer, vanes natural steel color.

Over-all length: 4 3/4 inches (may vary due to type of delay container used).

Material of construction: Brass except for steel striker, steel retaining ball, and steel spring or fuze may be steel throughout.

Position and method of fixing in bomb: Screwed clockwise into nose and secured by lock nut.

No anti-withdrawal devices used.

Components of explosive train: Primer flash cap and delay train incorporated in delay container.

Fuzes likely to be found with: None.

Delay times: May be varied by changing type of delay container.

Threads: 1 3/32 inches in diameter; 15 threads per inch.

Description: The fuze consists of three parts: The upper body contains the arming spindle; the lower body contains the steel striker; and the powder relay container which screws into the lower body portion. The spring loaded striker is held in position by a steel ball which rests on the shoulder in the lower body portion and is prevented from moving inward by the arming spindle. A primer flash cap is located in the lower body portion.

Operation: On release from the aircraft, the arming vanes rotate and fall free. The arm-ing spindle is withdrawn from the striker, allowing the locking ball to fall inward. The stri-ker now moves forward under spring action and pierces the flash cap, setting off the powder train which eventually sets off bursting charge.

Remarks: Fuze may be constructed of either brass or steel.

This fuze is an aerial burst fuze for the Type 2 No. 6 Mk 21 container and for Type 0 Pa-rachute Flare Model 1. When used in the Mk 21 container the D-4 (a) is designated Type 3 Initiating Mechanism and has a longer base to house a different delay train.

Figure 136 – D-4 (a) Bomb Fuze.