A fire bomb is a thin-skinned container of fuel gel designed for use against dug-in troops, supply installations, wooden structures, and land convoys. Fire bombs rupture upon impact and spread burning fuel gel on surrounding objects. One or more igniters and fuzes are used to ignite the fuel gel mixture upon impact. Fire bombs are used primarily for low level attacks.
The Mk 77 Mod 4 fire bomb holds approximately 75 gallons of fuel gel mixture and weighs approximately 500 pounds when filled.
The container is cigar-shaped, non-stabilized (will tumble end over end when released from the aircraft), lightweight, and is made of aluminum. It has a 14-inch suspension between the lugs and provides two filler holes, which are 31 degrees down from the top of the container. The filler holes are covered by filler caps, which are secured by retainer rings. The filler caps prevent foreign objects from getting inside the container during shipping and storage, and provides a sealed closure after the container is filled with fuel gel before fuzing. The filler holes also provide for the installation of the primary fuses. During fuzing procedures, the filler caps are removed and replaced by igniters, which seals the closure.
The primary fuzing system consists of the igniter Mk 273 Mod 0 with the M918 fuze or the initiator Mk 13 (igniter Mk 273 Mod 1 with the Mk 343 fuze). The Mk 77 Mod 4 also has provisions in the nose and tail for an alternate fuzing system using the AN-M173A1 fuze and AN-M23A1 igniter.
Functional Description
When the fire bomb is released from the aircraft, the arming wires are pulled from the fuzes, allowing the fuzes to become armed. When the bomb impacts the target or the ground, the container will rupture, disbursing the fuel gel mixture over the area. The fuzes detonate, rupturing the igniters, which , in turn, ignites the gel mixture.
Fuel Gel Mixture
Fire bomb fuel gel mixture, formerly called napalm, is a mixture of fuel and gelling solution that produces a thickened mixture. The gel should be stringy and sticky and readily adhere to most surfaces. The fuel gelling system consists of a fuel gelling unit, drums of gelling solution, aviation gas, mogas, JP-4, or JP-5 fuels.
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