Final protective fire

Final protective fire refers to a tactical plan for a military unit, typically infantry, to protect itself in defense against attack. The plan generally includes machine gun, mortar, and artillery fire prearranged to impede enemy movement across defensive lines or areas.

As the "final" in the name implies, it is the last resort in defensive plans, normally involving artillery and/or machine gun fire 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.

In the event FPF fails to stop the enemy advance, hand to hand combat then becomes of essential importance, with combative training being implemented, and any sort of ordered retreat to previously prepared positions becoming unfeasible.

Sources

http://usmilitary.about.com/od/glossarytermsf/g/finalprotfire.htm