FMU-139B/B Bomb Fuze is an electronic impact/impact
delay fuzing system designed for use by both the U.S.
Navy and Air Force in the MK 80 series and M117 low drag
and high drag, guided or unguided, high-explosive bombs.
It is manufactured by Alliant
Techsystems. In addition to impact/impact delay, the
fuze is capable of accepting a signal from a separate
proximity sensor. The fuzing system meets all U.S. Navy
and Air Force requirements, including the safety
criteria of MIL-STD-1316.
Key features of the FMU-139B/B include ease of
installation and preparation for flight, compatibility
with the proximity sensor fire signal, ability to sense
a high-drag delivery, and the ability to manually set
the arming and event times prior to takeoff through its
microcomputer (Air Force requirement) or electrically
set them by cockpit selection at bomb release (Navy
In the Navy application, power is transmitted to the
fuze from the AN-AWW series Fuze Function Control Set (FFCS)
at release from the aircraft. In the Air Force
application, power is provided by the FZU-48/B
air-driven turbine alternator, which is lanyard
activated upon release from the aircraft.