Light Machine Guns are used for suppression in Operation Flashpoint: Red River.
To suppress enemies, fire close to them and they will often dive to the ground or crouch and wait for the fire to stop. This makes them easy targets. The Automatic Rifleman can have a Special ability which increases the amount of tracers to improve suppression on LMGs.
Occasionally, other marines can be seen suppressed, but since the player can choose to move out under fire, suppression has less of an effect.