We’re going to continue our discussion of Machine Gun Theory. Specifically, we will discuss what the classes of fire are, and discuss them each in order. The old mnemonic device had the classes of fire ‘good to go’: FM 3-22.68, dated July 2006 lists the classes of fire as with respect to the Ground, Target, and Gun.
The classes of fire with respect to the ground are two-fold: grazing and plunging. Grazing fire is achieved with the machine gun when the center of the cone of fire does not rise more than one meter above the ground. This also means that there is danger space generally between the muzzle and the threat. This class of fire is primarily used as a final protective line (FPL) in the defense. The maximum distance for light and medium machine guns (M249/M240) is 600 meters.
Plunging fire occurs when there is little to no danger space between the muzzle of the machine gun and the threat. This means that the trajectory of the projectiles from the machine gun rises more than 1.8 meters (average height of a standing soldier) from the ground, allowing for potential movement of enemy or friendly forces between the gun and the beaten zone. This generally occurs at long range, when firing from high ground into the low ground, when firing onto abruptly rising ground, or when firing across uneven terrain. Figure 5-3 illustrates this.
Classes of fire with respect to the target are the next class we will discuss. Fire with respect to the target is how the beaten zone intersects with the threat’s movement or position. The Classes of fire with respect to the target include frontal, enfilade, oblique, and flanking.
Classes of fire with respect to the gun are the last class of fire we will discuss. This class of fire is how moving (or not moving) the machine gun in a certain direction causes the beaten zone to move across the sector of fire. There are five different types of fire: these include fixed, searching, traversing, traversing and searching, and free gun. Figure 5-6 illustrates this.
Of the three classes of fire, there is only one that the Machine Gunner has direct control over without moving his position; that is with respect to the gun. The ground and the target both require the machine gunner to move his location to affect a change to those classes.
To sum up; we’ve discussed the classes of fire with respect to the ground, target and gun, we’ve outlined what the 2 classes of fire are for the ground, the four classes of fire are for the target, and the five classes of fire are for the gun. We will continue our discussion about machine guns with a discussion about machine gun math.