First lieutenant

First Lieutenant is a junior commissioned officer of the UNSC Marine Corps and Army, equal in rank to Lieutenant, Junior Grade in the UNSC Navy. They can be given command of platoons or expansive companies, such as the case of 1st Lieutenant Melissa McKay in Halo: The Flood.

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".