The term Final Protective Fire really means exactly what it says. It is used by combat arms units conducting defensive operations. This is a term that you do not want to hear during combat because if you do you are in some serious trouble.
Normally you will fire the FPF when you are being overrun. When you fire the FPF you shot everything that you have left as fast as you can. Infantry ring customers know this term very well. When the Field Artillery Observer sees that his infantry is being overrun he will call the artillery and ask them to fire the FPF.
The Field Artillery Fire Direction Officer has the FPF plotted as a line on the ground. He knows that the line is very close to the friendly infantry ring customers so he has the Fire Direction Center to give the guns the command to “Use Gunner’s Quadrant.” Each gun chief knows to use the gunner’s quadrant which is a precision instrument. This insures extra accuracy so that no friendly troops are hurt by friendly artillery. The artillery military ring customers know that they need to fire everything that they have as fast as they can to help out their infantry brothers.