The Mod 0 and Mod 1 fuzes are installed in the Mk
20 Mods 2,3,4, and 6 bomb clusters. The Mod 0 fuze
without the option time wire configuration is used only
in the Mk 20 Mod 2 bomb cluster. The Mk 339 Mod 0
and Mod 1 fuzes are installed in the bomb clusters
during assembly by the manufacturer; therefore, the
following information on these fuzes is limited.
The Mk 339 Mod 1 fuze is similar to the Mod 0 fuze.
Several improvements are discussed in the following
The primary and option functioning delays are
preset during assembly at the factory for both the Mod
0 and Mod 1 fuzes. The fuzes are preset at 1.2 seconds
for primary delay, and the option delay is preset at 4.0
seconds. The Mod 0 fuze (without the option time wire)
is preset at 4.0 seconds on the option delay. The primary
delay is not used on this fuze The primary delay is set
at zero time.
You already know the primary and option delays for
the Mod 0 and Mod 1 fuzes are preset at the factory.
These time delays can be reset during weapon
preparation to meet various tactical requirements. The
primary and option time delays for the Mod 0 fuze can
be adjusted from 1.2 to 50.0 seconds by adjusting the
primary time setting dial and the option time setting dial,
respectively. The functional delays for both the primary
and option modes of the Mod 1 fuze can be adjusted
from 1.2 to 100 seconds in the same manner.
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 for both the Mod 0 and Mod 1 fuzes. If the
arming wire has been accidently pulled during handling,
the fuzes shift to the option mode. Once the option wire
is pulled, the Mod 0 fuze is committed to the option
mode and cannot be reset to the primary mode.
However, the Mod 1 fuze can be reset to the primary
mode by reinstalling the option time wire.
The fuze safe/arm indicator (callout 1 of figs. 1-2
and 1-3) provides external evidence of arming (EEA)
for the Mk 339 Mod 0 and Mod 1 fuzes. The fuze
safe/arm indicator is viewed through the indicator
observation window in the upper nose fairing. Mod 0
fuzes (lots 1 through 14) are in a safe condition when
the tip of the indicator pin does not extend into the
bubble (fig. 1-4, view A). The fuze is in an armed
Figure 1-4.Mechanical time fuze Mk 339 safe/arm indicator pin in safe and armed positions,