First Lieutenant is a junior commissioned officer of the Marine Corps and Trooper Corps, equal in rank to Lieutenant, Junior Grade in the Navy. They can be given command of platoons or companies, but are normally given positions as second in command in regards to companies.
A Second Lieutenant usually receives a promotion to First Lieutenant after 18 to 24 months service. In informal settings, First Lieutenants are referred to simply as "Lieutenant". First Lieutenant was one of the ranks commonly given to Genins while they were participating with the Corps for training. Genins using this rank were normally assigned second in command position unless they had prior command experience or were specially gifted.