A lieutenant, junior grade or its Commonwealth equivalent, sublieutenant, is the second lowest rank of commissioned officer in most naval organizations.
In the British Royal Navy, a passed midshipman awaiting promotion often elected to become a master's mate, normally an experienced petty officer who assisted the sailing master. Though formally the rating did not lead to promotion to lieutenant, master's mates were paid more than any other rating and were the only ratings allowed to command any sort of vessel. A midshipman who became a master's mate got an increase in pay from £1 13s 6p to £3 16s per month, but initially reduced his chances at a commission. Over time, however, service as a master's mate became a normal part of the path to a commission. The situation caused some confusion during the last part of the 18th century, when two parallel roles - master's mates trying to become masters, and former midshipmen working toward a commission - held the same title and responsibilities aboard ship.
By the first years of the 19th century, the prefix "master's" was dropped for passed midshipmen, to distinguish them from master's mates in the navigator's branch. In 1824 two further grades were also introduced, consisting of master's assistants and second-class volunteers. These corresponded to midshipmen and first-class volunteers respectively in the executive line. From this point, passed midshipmen had the rating master's mate, abbreviated as mate, and prospective masters had the rating master's assistant. These changes helped eliminate the confusion caused by the mingling of midshipmen in the navigator's branch.
In 1838 a Royal Commission, presided over by the Duke of Wellington, recommended the institution of the rank of mate as an official step between midshipman and lieutenant. In 1861 mate was abolished in favor of sub-lieutenant.
In Starfleet, a lieutenant junior grade (or as it is styled 'lieutenant (jg)') is senior to an ensign but immediately subordinate to a full lieutenant. Most lieutenants, junior grade, have been on active duty for at least six months as an ensign before becoming eligible for promotion consideration by the Starfleet Bureau of Personnel.
Starfleet used the following rank insignia to denote this rank of officer:
Some military and paramilitary groups use the rank "lieutenant (jg)" in their organizations:
Lieutenants (jg) within the MSS are often placed in command of auxiliary starships, such as cargo runabouts. They may also serve on transports or light freighters as First Officer or as a senior Division Officer aboard. On larger vessels, they may see service as a Division Officer or Assistant Division Officer.
The Bajoran Defense Force Navy uses the alternative equivalent, Sublieutenant:
Rikon Defense Force
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