Lieutenant (junior grade), commonly abbreviated as LTJG or, historically, Lt. (j.g.) (as well as variants of both abbreviations), is a junior commissioned officer rank of the United States Navy, the United States Coast Guard, the United States Public Health Service Commissioned Corps, and the National Oceanic and Atmospheric Administration Commissioned Officer Corps (NOAA Corps). LTJG has a US military pay grade of O-2, and a NATO rank code of OF-1a. The rank is also used in the United States Maritime Service. The NOAA Corps's predecessors, the United States Coast and Geodetic Survey Corps (1917-1965) and the Environmental Science Services Administration Corps or ESSA Corps (1965-1970), also used the rank.
Lieutenant, junior grade, ranks above ensign and below lieutenant and is equivalent to a first lieutenant in the other uniformed services (the Army, Marine Corps and Air Force) and sub-lieutenant in the Royal Navy and the navies of many Commonwealth countries.
Promotion to LTJG is governed by Department of Defense policies derived from the Defense Officer Personnel Management Act of 1980. DOPMA guidelines suggest all "fully qualified" ensigns should be promoted to LTJG. The time for promotion to LTJG is a minimum of two years after commissioning in the Navy or 18 months in the Coast Guard. Lieutenants, junior grade typically lead petty officers and non-rated personnel, unless assigned to small aircraft or on staff duty. A LTJG's usual shipboard billet is as a division officer.