Nose fuzes of this type are vane operated and delay armed. Fuzes AN-M103A1, AN-M139A1, and AN-M140A1 are fast arming and should not be used on high performance type aircraft presently in use. Action can be either instantaneous or delayed by presetting a setting pin. The air travel to arm distance is governed by the size of the bomb and the type of arming vane used. Structurally similar, these fuzes differ only in their firing delay elements. Fuzes M163, M164 and M165 are similar to nose fuzes AN-M103A1, AN-M139A1, and AN-M140A1, respectively, except in point of increased arming time. Further increase in arming time can be provided for fuze M163 by use of arming vane M3, which has its angle of vane surface twisted to 75°.
These fuzes contain two explosive trains: one for delay action and another for instantaneous action. The delay action explosive train consists of a primer, a delay element, a relay, a detonator, a booster lead-in, and a booster. The primer and delay element assembly, containing the delay element and relay, are assembled in the fuze body and are sealed as a protection against moisture. The instantaneous explosive train consists of a detonator, a booster lead-in and a booster. The same detonator is used in both explosive trains. It is aligned with one of the explosive trains during arming operations ; its final position depends upon the position of the setting pin.
Primer M39A1, Detonator M20, Relay M6.
The booster contains 1.9 oz of Tetryl.
MIL-HDBK-146, Fuze Catalog (1982)
TM 9-1385-51, Ammunition (Conventional) for Explosive Ordnance Disposal (1967)
TM 9-1325-200, Bombs and Bomb Components (1966)
TM 3-400, Chemical Bombs and Clusters (1957)
OP 1664, Volume 2 - US Explosive Ordnance (1947)
USNBD - Bombs and Fuzes, Pyrotechnics (1945)