Lieutenant colonel (United States)

In the United States Army, U.S. Marine Corps, and U.S. Air Force, a lieutenant colonel is a field grade military officer rank just above the rank of major and just below the rank of colonel. It is equivalent to the naval rank of commander in the other uniformed services.

The pay grade for the rank of lieutenant colonel is O-5. In the United States armed forces, the insignia for the rank consists of a silver oak leaf, with slight stylized differences between the Army/Air Force version and the Navy/Marine Corps version.

Promotion to lieutenant colonel is governed by Department of Defense policies derived from the Defense Officer Personnel Management Act (DOPMA) of 1980 for officers in the Active Component and its companion Reserve Officer Personnel Management Act (ROPMA) for officers in the Reserve Component (e.g., Reserve and National Guard). DOPMA guidelines suggest 70% of majors should be promoted to lieutenant colonel after serving a minimum of three years at their present rank and after attaining 15–17 years of cumulative commissioned service.

While often written as "Lt. Colonel" in orders and signature blocks, as a courtesy, lieutenant colonels are addressed simply as "colonel" verbally and in the salutation of correspondence. The U.S. Army uses the three letter abbreviation "LTC." The United States Marine Corps and U.S. Air Force use the abbreviations "LtCol" and "Lt  Col" (note the space) respectively.

...
Wikipedia