Lieutenant

Lieutenant is a junior commissioned officer rank in the UNSC Navy, equal in rank to Captain in the UNSC Marine Corps and in the UNSC Army.

Title
This rank is sometimes referred to as "Full Lieutenant" to distinguish it from the subordinate rank of Lieutenant, Junior Grade.

While Lieutenant is a rank specific to the UNSC Navy, the title "Lieutenant" is often used to refer to several ranks in the UNSC Defense Force:

Navy Marine Corps and Army
 * Lieutenant
 * Lieutenant, Junior Grade
 * First Lieutenant
 * Second Lieutenant

Trivia

 * Lieutenants are often addressed by UNSC personnal as "El-Tee", an example being Melissa McKay in Halo: The Flood.