The Marine Corps rifle platoon contains three rifle squads. Each squad is led by a sergeant who has three fire teams working for him, each led by a corporal. The fire team leader typically carries the M203 grenade launcher slung under his M16. Operating under him are the automatic rifleman, assistant automatic rifleman, and rifleman. The Army platoons contain smaller squads. An Army rifle squad leader is typically a sergeant or staff sergeant who leads two four-man fire teams. Each Army fire team consists of a team leader, an automatic rifleman, a grenadier, and a rifleman. Note that the Army squad is using a dedicated grenadier in place of an assistant automatic rifleman. Typically, one rifleman in each squad will be a squad designated marksman, a specially trained shooter who engages targets at long range. Also, the Army has an additional squad in each platoon, the infantry weapons squad. This squad has teams dedicated to the M240B machine gun and the Javelin missile system.
MBV Note: For militia, I have always preferred the larger 13 man USMC squad of three fire teams of four plus a squad leader, with a designated marksman in each fire team to take up for the slack of no permitted base-of-fire full auto weapons. Of course, I always assumed that after the balloon went up, there would also be one rifle grenadier per fire team as well.