Table 1-2.—Indications for Determining Conditions of M904E3/4 Nose Fuzes

A3. The time required for a fuze to detonate after impact or a preset time is known as the functioning time. A4. The distance along the trajectory that a bomb travels from the releasing aircraft in an unarmed condition is known as the safe air travel (SAF). A5. The two basic classes of fuzes are electrical and mechanical. A6. The force used to initiate the mechanical fuze is like the hammer and primer used to fire a rifle. A mechanical force drives a striker into a sensitive detonator. A7. An electrical impulse initiates an electrical fuze. A8. The three special safety features incorporated into fuzes are detonator safe, shear safe, and delay arming features. ARMING DELAY TIMES.—Arming delay times are inscribed into the face of the forward nose retaining ring. A white indexing line is scribed on the knurled delay setting knob below the arming vane. The white indexing line must be matched to one of the indicated arming times to select the desired arming delay. To select the required arming delay time, depress the setting index locking pin and rotate the knurled arming delay setting knob until the white indexing line is aligned with the desired arming delay time stamped on the nose retaining ring. The 2- and 4-second arming times are for use with retarded weapons, and are only set by removing the stop screw located next to the setting index locking pin. Never try to reinstall the stop screw when either of these two settings are used. The stop screw may be reinstalled at any delay setting of 6 seconds or more. IDENTIFICATION OF ARMED FUZES.— There are three conditions of the M904 fuze—safe, partially armed, and fully armed. You can verify the fuze conditions by looking through the two observation windows in the fuze body (fig. 1-1). To check the fuze condition, hold the fuze vertically and look through the windows perpendicular to the fuze body. Look at table 1-2. It shows you what you would see through the observation windows of the M904E3/4 fuze at various time settings and fuze conditions. Also, check the M904E4 to make sure the thermal sleeve is firmly bonded to the fuze collar and is not cracked. NOTE: If the safe condition of any fuze is in doubt, explosive ordnance disposal (EOD) personnel should be notified immediately. 1-5 Condition Time Setting Upper Window Lower Window Safe 18 Seconds White number "18" on green background. Vacant or dark in color. 6 Seconds White number "6" on green background. Partially Armed 18 and 6 Seconds Green background with no numbers visible. (If numbers appear at other than "18" or "6" second setting or if numbers do not match settings, fuze is partially armed.) Vacant or dark in color. Armed Any setting. (Time setting cannot be changed.) *Red with black letter "A." (Some green may show at top of window.) *Red with black Letter "A." Table 1-2.—Indications for Determining Conditions of M904E3/4 Nose Fuzes