In Star Trek: The Motion Picture, James Kirk holds the rank of admiral when he takes command of Enterprise.
Kirk has been promoted from captain and serves as Chief of Starfleet Operations before the V’Ger crisis. He returns to active command when Starfleet orders the Enterprise to investigate the enormous energy cloud approaching Earth. Kirk then assumes control of the refitted Constitution-class starship, displacing Captain Willard Decker.
This promotion creates one of the film’s central tensions. Kirk is experienced and determined, but his decision to resume command leaves Decker in the role of executive officer and complicates their working relationship. The film’s plot therefore combines a large-scale alien mystery with a dispute over authority aboard the Enterprise.
Kirk later returns to the captain’s rank in subsequent films. That change can cause confusion when viewers remember him primarily as captain, but he is explicitly an admiral during the events of The Motion Picture.