Final protective fire refers to a tactical plan for a military unit, set up by the forward observer in support of the infantry, to protect itself against overwhelming attack. A final protective fire is an immediately available preplanned barrier of direct and indirect fire designed to provide close protection to friendly positions and installations by impeding enemy movement into defensive areas. The size of the FPF depends on the number and type of weapons firing (e.g. FPF size for one battery of 155mm howitzers is 300m X 50m). The supported maneuver commander designates the location of the FPF and it is adjusted into place by the forward observer. Normally, the FPF is within 200 to 400 meters of friendly positions and is integrated into the final protective line of the maneuver unit.

As the "final" in the name implies, it is the last resort in defensive plans, involving artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 integrated with small arms and heavy machine gun

Heavy machine gun

The heavy machine gun or HMG is a larger class of machine gun generally recognized to refer to two separate stages of machine gun development. The term was originally used to refer to the early generation of machine guns which came into widespread use in World War I...

 fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

directed dangerously close to friendly defensive positions that are at risk of being overrun by the enemy. A request for final protective fire generally has absolute priority over any other kind of requests.