Functional Description The M904 fuze arms and functions by the rotation of the arming vane and alignment of its internal components. When the fuze is released from the aircraft, the fuze arming wire is withdrawn from the fuze arming vane, and the arming vane is rotated by the airstream. Arming vane rotation is controlled by the constant arming action of the governor in the fuze. The arming vane continues to rotate until the preselected arming delay period (2 to 18 seconds) elapses (ends). Once the arming delay period elapses, the firing train is in full alignment and ready to function. At impact, the forward part of the fuze body drives the striker body and firing pin down into the M9 delay element.  After  the  proper  delay,  the  M9  delay  ignites the relay, detonator, lead, and booster, which sets off the main charge. REVIEW NUMBER 2 Q1. What kind of fuze is the M904? Q2. What bomb series is the M904 fuze used with? Q3. The  M904  fuze  has  ______  arming  delays, which  you  can  set  for  2  to  18  seconds  in ______    increments;    there    are    any    com- bination   of   ____   functioning   delays   from instantaneous to 250 milliseconds. Q4. The M904 is thermally protected. Why is this important? Q5. Describe  the  means  you  use  to  check  the condition of the M904 fuze. Q6. If you can't tell if a fuze is "safe," you should notify ___________. Q7. The M904 arms and functions by __________________. 1-6 13 12 17 11 10 9 8⁷ 18 14 2 3 16 15 1 6 5 4 NOTE TOP OF BOMB CLUSTER ROTATED 45 DEGREES CLOCKWISE FOR CLARITY A A 1. Fuze safe/arm indicator 2. Timer starting pin 3. Timer starting pin bracket 4. Option time setting adjustment 5. Primary time setting adjustment 6. Band release stud and nut 7. Fuze arming wire 8. Safety pin assembly 9. Impeller 10.    Impeller band assembly 11.    Time setting observation window 12.    Option time pin 13.    Indicator observation window 14.    Nose fairing (reference) 15.    Option time wire 16.    Retainer slide 17.    Clip 18.    Safety pin assembly guide tube Figure 1-2.—Installed mechanical time fuze Mk 339 Mod 1 (with option time wire bomb clusters Mk 20 Mods 3, 4, and 6.