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