MK 339 MOD 1 MECHANICAL TIME FUZE
The Mk 339 Mod 1 mechanical time fuzes (fig.
1-2) are used with dispenser weapons and have the
The Mod 1 fuze is installed in the Mk 20 Mods 3, 4,
and 6 bomb clusters. The Mk 339 Mod 1 fuze is
installed in the bomb clusters during assembly by the
manufacturer; therefore, the following information on
this fuze is limited.
REVIEW NUMBER 2 ANSWERS
The M904 is a detonator-safe, mechanical
impact nose fuze.
The M904 series fuze is used with Mk 80
The M904 fuze has nine arming delays, which
you can set for 2 to 18 seconds in 2-second
increments; there are any combination of six
functioning delays from instantaneous to 250
It is important for the M904 to be thermally
protected because it increases the "cook-off"
time of bombs subjected to intense heat or
There are three conditions of the M904 fuze
safe, partially armed, and fully armed. You
can check for these conditions by looking in
the two observation windows in the fuze body.
If you can't tell if a fuze is "safe," you should
notify explosive ordnance disposal (EOD)
The M904 arms and functions by rotation of
arming vanes and alignment of internal
The primary and option functioning delays are
preset during assembly at the factory. The fuze is preset
at 1.2 seconds for primary delay, and the option delay is
preset at 4.0 seconds.
You already know the primary and option delays
for the fuze is preset at the factory. These time delays
can be reset during weapon preparation to meet various
tactical requirements. The functional delays for both
the primary and option modes of the Mod 1 fuze can be
adjusted from 1.2 to 100 seconds.
You can tell if the fuze has shifted from the primary
to the option mode by the functional mode indicator.
You do this by checking the time setting observation
window. If the arming wire has been accidentally
pulled during handling, the fuzes shift to the option
mode. Once the option wire is pulled, the fuze can be
reset to the primary mode by reinstalling the option
The fuze safe/arm indicator (callout 1 of figs. 1-2)
provides external evidence of arming (EEA) for the Mk
339 Mod 1 fuze. The fuze safe/arm indicator is viewed
through the indicator observation window in the upper
nose fairing. There is a layer of green foil at the base of
the indicator bubble. The fuze is in a safe condition
when the green foil is intact (fig. 1-3, view A), and it is
armed when the green foil is pierced by the indicator
pin (fig. 1-3, view B).
The following paragraph describes the sequence of
events that must occur for Mk 339 fuze to function.
MOD 1 (WITH OPTION TIME WIRE).This
fuze is physically and functionally the same as the fuze
MK 339 MOD 1 FUZE SAFE/ARM
INDICATOR PIN IN SAFE POSITION
MK 339 MOD 1 FUZE SAFE/ARM
INDICATOR PIN IN ARMED POSITION
Figure 1-3.Mechanical time fuze Mk 339 safe/arm indicator pin in safe and armed positions.