Corporal
From Starbase 900 Wiki
Corporal is the fourth enlisted rank in the Starfleet Marine Corps, ranking immediately above Lance Corporal and immediately below Sergeant. Corporal is the lowest grade of non-commissioned officer in the Marine Corps, though promotion to corporal traditionally confers a significant jump in authority and responsibility compared to promotion from private through lance corporal. Theoretically, Marine Corporals generally serve as "fire-team leaders," commanding a 4-man team or unit of similar size.
In practice, however, the billet of fire team leader is generally held by a Lance Corporal, while Corporals serve in the squad leader billet that would normally be held by a Sergeant in infantry units. In support units, they direct the activities of junior Marines and provide technical supervision. Due to its emphasis on small-unit tactics, the Marine Corps usually places Corporals in billets where other services would normally have an E-5 or E-6 in authority. Similarly, the term "Strategic Corporal" refers to the special responsibilities conferred upon a Marine Corporal. Corporal is equivalent to the rank of Petty Officer Third Class.