Lieutenant (junior grade)

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. 
The rank is also used in the United States Maritime Service.