FMU-139

FMU-139. The FMU-139 is a family of advanced electronic fuzes developed in the United States for use in a wide array of air-dropped munitions. Designed primarily at Picatinny Arsenal, these fuzes provide multiple functioning modes to enhance weapon effectiveness against diverse targets. They are a critical component within the United States Department of Defense's inventory and are widely used by NATO allies.

Overview

The development of the FMU-139 series began in the 1970s at Picatinny Arsenal in response to a need for more reliable and versatile fuzing options for modern aerial bombs. It was engineered to replace older mechanical fuzes like the FMU-81 and FMU-113 with a solid-state electronic system. The fuze's introduction marked a significant advancement in weapon safety and target effects, becoming a standard component for general-purpose bombs such as the Mk 80 series. Its adoption by the United States Air Force and United States Navy standardized fuze logistics across multiple platforms.

Design and Function

The FMU-139 is an electronic, programmable fuze that offers selectable arming delay and functioning delay settings, allowing aircrews to tailor weapon behavior for specific mission profiles. Its internal circuitry is powered by a thermal battery activated upon weapon release from an aircraft like the F-16 Fighting Falcon or F/A-18 Hornet. Key design features include all-ways sensing technology for reliable impact detection and robust environmental sensing to prevent accidental detonation. The fuze interfaces with aircraft stores management systems and can be set for instantaneous impact, delay, or proximity burst modes to optimize effects against targets such as hardened aircraft shelters or area targets.

Variants

Several variants have been produced to meet evolving operational requirements and to interface with different weapon systems. The FMU-139A/B was an early production model, while the FMU-139C introduced improved safety features and reliability. The FMU-152/B, part of the Joint Programmable Fuze family, represents a significant evolution with enhanced programmability for use with Joint Direct Attack Munition kits. Other related fuzes in the lineage include the FMU-143 and the FMU-156/B, which offer specialized capabilities for bunker buster munitions and other penetrating weapons.

Operational History

The FMU-139 series has seen extensive use in every major conflict involving the United States Armed Forces since its introduction. It was employed in large numbers during the Persian Gulf War on bombs dropped by aircraft like the F-117 Nighthawk and B-52 Stratofortress. Subsequent use continued through operations in Kosovo, Afghanistan, and the Iraq War. Its reliability and flexibility have made it a cornerstone for precision-guided munition and dumb bomb deliveries, contributing to missions conducted by Coalition forces and NATO air arms.

Specifications

The fuze is designed to meet stringent MIL-STD requirements for shock resistance, temperature tolerance, and electromagnetic pulse hardening. It is qualified for use with bombs ranging from the Mk 82 to the Mk 84 and BLU-109. Physically, it conforms to standard MIL-SPEC dimensions for installation in bomb fuze wells. Key performance parameters include multiple delay settings typically ranging from milliseconds to several seconds, with arming sequences governed by safe separation criteria after release from aircraft like the F-15 Eagle.

Category:American fuzes Category:Military equipment introduced in the 1970s