EXPLOSION IN TURRET TWO
Investigation Continued

               corresponding material from experimental 8” HC detonations.  Principal findings include the following:

    a.    Footprints in the bore from the projectile band score establish projectile location at the instant of detonation as approximately 0.1” forward of the estimated seating position.

    b.    Footprints in the bore from the expanded nose of the projectile conform to the above location, are similar in appearance to those of an experimental nose-initiated high-order detonation, and are recognizably different from those for other types of experimental detonations.

    c.    Location of the largest part of the liner bulge relative to the position of projectile detonation conforms to experimental nose initiation, and differs from that for other types of experimental initiations.

    d.    Metallurgy and fracture patterns seen in longitudinal sections of projectile and tube fragments correspond with conditions resulting from an experimental nose-initiated high order detonation, and differ from those for other types of experimental detonations.

DISCUSSION

The Casualty

26.       The evidence noted in the preceding paragraph appears to establish that the casualty resulted from a nose-initiated high order detonation, which occurred within a fraction of a millisecond after propellant ignition.  (This supersedes our initial judgment, and that of other experienced observers at Subic, that the detonation was low order, about .007 seconds after detonation, hence most probably caused by a defective projectile base seal.)

27.       All experience with D-loaded projectiles seems to indicate that such a detonation, within that reaction time, could result only from initiation by the tetryl booster of the nose ADF.

28.       In our judgment, the only realistic explanation as to how the latter could have occurred must include the requirement that the fuze rotor (which carries the primer) was in the armed position before the gun was fired.  This is because we understand that tests have demonstrated that accidental firing of the ADF primer, by whatever cause, will not fire the booster unless the rotor is armed; and we visualize no mechanism for firing the ADF booster, within the reaction time of this casualty, except by firing the ADF primer.  The possibility that the rotor was in fact armed as here postulated is supported by the evidence note in paragraph 16.

            (page 9)