condition when the indicator pin extends into the bubble (fig. 1-4, view B). On newer models (lots 15 and above of Mod 0 and Mod 1 fuzes), 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. 1-4, view C), and it is armed when the green foil is pierced by the indicator pin (fig. 1-4, view D). Functional Description The following paragraphs describe the sequence of events that must occur for Mk 339 fuzes to function. MOD 0 (WITHOUT OPTION TIME WIRE).— When the Mk 20 bomb cluster is released in flight, an impeller band assembly secures the impeller until the fuze arming wire is pulled out. As the weapon is released from the aircraft, the arming wire is pulled from the impeller band assembly, freeing the air-driven impeller. The arming wire also passes through a time starting pin, which initiates the fuze timing mechanism when the arming wire is pulled out. The airstream rotates the impeller, which physically aligns the firing train, and allows the fuze to detonate at the preset time. MOD 1 (WITH OPTION TIME WIRE).— This fuze is physically and functionally the same as the fuze described in the preceding paragraph except that an option wire is installed If the pilot selects the primary mode of delivery when the weapon is released from the aircraft, only the arming wire is pulled out and the primary mode of the fuze is initiated. If the pilot selects the option mode of delivery, both the arming wire and the option wire are pulled out, initiating the option time mode of the fuze. If only the option time wire is pulled out on airborne release, the fuze will dud. Both the fuze arming wire and option wire must be pulled out for the fuze to function in the option mode. Q1. Q2. Q3. Q4. REVIEW NUMBER 3 What bombs are used with the Mk 339 mechanical time fuze ? List the characteristics shared by Mod 0 and Mod 1 of the Mk 339 fuze. The primary and option delays of Mod 1 and Mod 0 fuzes are set at the factory. What means can be used to change the settings for tactical requirements? How can you tell if the fuze has shifted from the primary to the option delay? Q5. Q6. Describe what you will see in the observation window of a Mk 339 Mod 0 fuze for the conditions listed below: Safe Armed Describe what you will see in the observation window of a Mk 339 Mod 0 (lots 15 or above) or Mod 1 fuze for the conditions listed below: Safe Armed MK 346 MOD 0 MECHANICAL LONG-DELAY TAIL FUZE The mechanical long-delay fuze Mk 346 Mod 0 is an all-mechanical clockwork fuze that is used in the tail well of the Mk 80 (series) LDGP bombs. The functioning delays are preselected for the total number of hours, in increments of 15 minutes. The range of the functioning delay time is from 30 minutes to 33 hours. Description The Mk 346 fuze (fig. 1-5) is approximately 6 3/8 inches long and threaded for a 2-inch adapter booster well. For purposes of description, the terms outer end and base end are used. The outer end couples to the arming assembly; the base end fits into the adapter booster well. The input shaft and the delay functioning setting shaft are located on the outer end of the fuze. The input shaft is coupled directly to a centrifugal clutch that engages the speed reduction gear assembly when the input shaft reaches 1,200 rpm. The input shaft is fitted with a key that engages a locking slot to prevent accidental rotation. The key is automatically freed when the arming assembly is fitted to the input shaft. The delay function setting shaft is located in the outer end and may be rotated in either direction by a screwdriver. The setting shaft is coupled through a gear train to the dial, which is seen in the time delay observation window. The safe-armed band, visible through the safe-arm window, is coupled to the speed reduction gear. The red band covers the window when the input shaft and clutch have rotated 45 revolutions, thus completing the first stage arming. The red band starts to appear after the input shaft and the clutch have rotated approximately 22 of the required 45 revolutions. A slip clutch lets the 1-10