Physical Description

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. Physical Description The Mk 339 Mod 1 fuze is similar to the Mod 0 fuze. Several improvements are discussed in the following paragraphs. 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, 1-9