A final protective line is a predetermined line where interlocking bands of grazing fire are placed in order to stop enemy assaults. The elevation and direction of the fire are fixed and capable of being delivered under any condition of visibility.

Because of irregularities in the terrain, fixed machine gun fire cannot always produce the maximum effective grazing fire. Then the leader uses rifle fire to ensure that all the final protective lines are covered. Fire on the final protective line during periods of good visibility is aimed and adjusted fire. Under such conditions, the section leader will generally determine the rate of fire and may also give the order to cease firing. Under conditions of poor visibility, the battalion order may prescribe the rates of fire. In the absence of instructions, the usual rate of fire for a section on a final protective line is the rapid rate for the first 2 minutes, then the medium rate until ordered to cease firing.