The military rank of Lieutenant Colonel (LT. Colonel) was an army rank that was used by the Galactic Empire. A lieutenant colonel was subordinate to that of a full colonel, and was responsible for forces during a colonel's absence or served as an assistant to the colonel. Additionally, a lieutenant colonel served as the commanding officer of two battalions, and could serve in the capacity of ground commander when attached to an Imperial Navy task force.
The rank of lieutenant colonel was active by 14 BBY. At that time, of the Empire held the rank, and commanded Imperial forces on the planet Ryloth in the absence of Colonel Belkor Dray. During an Imperial mission to Ryloth undertaken by Galactic Emperor Palpatine and his enforcer Darth Vader to quell the Free Ryloth Movement, the ISD Perilous was attacked and shot down. After Colonel Dray resumed his command, the lieutenant colonel continued to assist their commanding officer.
In 5 BBY, the rebel group led by Saw Gerrera known as the Partisans undertook a scouting mission to Tamsye Prime. There, they infiltrated an Imperial documentary crew of the Imperial Broadcast, of which Lieutenant Colonel Senjax was a member of. Once the identity of the rebels was uncovered, the LT. Colonel laid a trap, though the Partisans were able to escape. Imperial forces launched an aerial strike of the area without regard for civilian lives in an attempt to stop the Partisans, resulting in Senjax being injured. In the aftermath, Senjax appeared on the HoloNet to recount the events on Tamsye Prime to the public, but fabricated and misinformed the viewers in order to hide the Empire's actions during the event.
During the Galactic Civil War, an invasion force that consisted of two battalions was led by Lieutenant Colonel Erle Hovlinn and was stationed on the Gladiator-class Star Destroyer Blood Ambition, the flagship of Captain Ralchio Nervi and his task force. During the war, Captain Nervi initiated the Battle of Xorrn against the Old Mandalorians and the Clan Assembly in order to hide his past in fear of being revealed as a Force-sensitive. LT. Colonel Hovlinn deployed his ground forces on Xorrn, but the Imperials were eventually defeated when the Allied Armada of the Alliance to Restore the Republic arrived.