Platoon
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A Platoon is a military unit used by the UNSC Marine Corps to organize its combat forces. Normally, a Platoon is composed of either three or four squads. A platoon can contain at least 30 to 50 troops.
Composition
Platoons are composed of anywhere from 30 to 50 troops, depending on the size and number of squads in the platoon. Depending on their purpose, a Platoon can have a varying number and specialty of its personnel. Using a United States Marine Corps platoon as an example, a Rifle Platoon usually encompasses three squads of riflemen, as well as a Navy medical Corpsman, a Platoon Commander (usually a First Lieutenant) and a Platoon Sergeant (usually a Staff Sergeant. If the UNSC uses a Weapons Platoon, then the squads are replaced by mortar section, assault section and medium machine gun section.
ODST platoons seem to have fewer members than the regular Marine units, possibly because they aren't as easily defeated in battle, making it more efficient to deploy them in smaller forces.