|There is more information available on this subject at Final protective fire on the English Wikipedia.|
Final Protective Fire, FPF for short, 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 heavy 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.
More or less often, "danger close" salvos are typically targeted within 100 or less meters of a friendly defensive position, making them dangerous to anything within the nearby radius.
During the Raid on New Alexandria, Kilo 40 ordered Kilo 26 to fire FPF One and Two to halt a SDV-class heavy corvette over the city. They were unsuccessful at destroying the target, however. This resulted in the evacuation path at Traxus Tower being destroyed by the Corvette's weapons, and prevented evacuation vessels from taking off without being shot by the ship. The evacuation was delayed until the Bullfrogs were able to secure a new route with the help of Noble Six, who stopped the Corvette with missile batteries.