Lieutenant junior grade (Star Trek)

Star Trek uniforms are worn by crew members in the Star Trek science fiction franchise. While the Star Trek television series and motion pictures feature various costumes, those worn by actors portraying enlisted personnel and officers from the fictitious organization Starfleet are the ones most closely associated with Star Trek costuming. Though design varied among the successive costume designers, the uniforms costumes and insignia remained consistent within any one series or film. Costumes were re-designed to improve appearance when filmed and to improve the comfort for actors. Deliberately mixing styles of uniforms from the various series was occasionally used to enhance the sense of time travel or alternative universes.

The rank system of the Star Trek universe resembles that of the United States Navy and the British Royal Navy in contrast to other science fiction franchises that use an army ranking system. In Star Trek: The Original Series (TOS) and Star Trek: The Motion Picture, ranks are indicated by sleeve stripes; in later movies based on The Original Series, ranks are indicated by pins on a shoulder strap and the left sleeve. In later television series, ranks are indicated by varying numbers of pips or bars on the individuals' uniform collars.

The insignia are worn on the left breast by all personnel. Originally gold with a black border, but the shape differed based on the ship or base to which the person was assigned as seen in TOS episodes "Court Martial", "The Doomsday Machine", etc. In the case of the Enterprise, the insignia was a delta or arrowhead shape. A black symbol within the insignia (the same for most shapes) also indicated the wearer's division — a star with an elongated top point indicated command, a circle crossed by an oval (as a ringed planet) science and medical, and an angular spiral (a galaxy shape) operations and engineering. In the second pilot, the science/medical and engineering/operations symbols were reversed ("Where No Man Has Gone Before"), and there were other slight variations between the insignia as used in the pilots and in the regular series.

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