The M904 fuze arms and functions by the rotation
of the arming vane and alignment of its internal
components. When the fuze is released from the
aircraft, the fuze arming wire is withdrawn from the
fuze arming vane, and the arming vane is rotated by the
airstream. Arming vane rotation is controlled by the
constant arming action of the governor in the fuze. The
arming vane continues to rotate until the preselected
arming delay period (2 to 18 seconds) elapses (ends).
Once the arming delay period elapses, the firing train is
in full alignment and ready to function.
At impact, the forward part of the fuze body drives
the striker body and firing pin down into the M9 delay
element. After the proper delay, the M9 delay ignites
the relay, detonator, lead, and booster, which sets off the
REVIEW NUMBER 2
What kind of fuze is the M904?
What bomb series is the M904 fuze used with?
The M904 fuze has ______ arming delays,
which you can set for 2 to 18 seconds in
______ increments; there are any com-
bination of ____ functioning delays from
instantaneous to 250 milliseconds.
The M904 is thermally protected. Why is this
Describe the means you use to check the
condition of the M904 fuze.
If you can't tell if a fuze is "safe," you should
TOP OF BOMB CLUSTER
ROTATED 45 DEGREES
CLOCKWISE FOR CLARITY
Fuze safe/arm indicator
Timer starting pin
Timer starting pin bracket
Option time setting adjustment
Primary time setting adjustment
Band release stud and nut
Fuze arming wire
Safety pin assembly
10. Impeller band assembly
11. Time setting observation window
12. Option time pin
13. Indicator observation window
14. Nose fairing (reference)
15. Option time wire
16. Retainer slide
18. Safety pin assembly guide tube
Figure 1-2.Installed mechanical time fuze Mk 339 Mod 1 (with option time wire bomb clusters Mk 20 Mods 3, 4, and 6.