Corporal

Corporal is a military rank that is used by most militaries. It is also used by some police forces or other uniformed organizations.
In the United States Army a Corporal is usually a fire team leader or second-in-command of a squad of soldiers. In the United States Marine Corps, Corporal is the rank for a team leader of a squad, machine gun team or the equivalent. 
It is equal in grade but senior by job title to specialist in the U.S. Army.