Lt. (jg)

Lieutenant junior grade (often abbreviated to lieutenant J.G. or simply J.G.), or junior lieutenant is a military rank, the equivalent of which is used by the service organizations of many civilizations. A naval rank in a small number of Earth's ancient navies (such as the US Navy), it is placed between ensign and full lieutenant. The rank is used primarily by the Federation Starfleet, although its Earth predecessor (from which it primarily takes its rank structure) may also have had this grade.

During certain points in its history, Starfleet has discontinued the rank of Lieutenant Junior Grade, promoting Ensigns directly to the full grade of Lieutenant. This was the case in the early 2270s, when Ensigns adopted the sleeve insignia of the former Lieutenant J.G. rank, the J.G. rank being done away with. Historical records also indicate that the Earth Starfleet did not use the rank during the 2150s.

It is unclear if the grade exists in other cultures' rank arrangements, although it may correspond to the Romulan rank of sublieutenant.