MK 339 MOD 1 MECHANICAL TIME FUZE

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 following characteristics: � Nose-mounted � Air-enabling � Detonator-safe 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 A1. The M904 is a detonator-safe, mechanical impact nose fuze. A2. The M904 series fuze is used with Mk 80 (series) bombs. A3. 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 milliseconds. A4. It is important for the M904 to be thermally protected because it increases the "cook-off" time of bombs subjected to intense heat or flame. A5. 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. A6. If you can't tell if a fuze is "safe," you should notify explosive ordnance disposal (EOD) personnel. A7. The M904 arms and functions by rotation of arming vanes and alignment of internal components. Physical Description 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 time wire. 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). Functional Description 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 1-7 GREEN FOIL INTACT INDICATOR BUBBLE GREEN FOIL PENETRATED RED TIP MK 339 MOD 1 FUZE SAFE/ARM INDICATOR PIN IN SAFE POSITION MK 339 MOD 1 FUZE SAFE/ARM INDICATOR PIN IN ARMED POSITION A. B. AOf0103 Figure 1-3.—Mechanical time fuze Mk 339 safe/arm indicator pin in safe and armed positions.