- "It's an old naval tradition. Whoever's in command of a ship, regardless of rank, is referred to as 'captain.'"
- "You mean if I had to take command, I would be called 'captain,' too?"
- "Cadet, by the time you took command, there'd be nobody left to call you anything."
- — Senior Chief Petty Officer Miles O'Brien and Cadet Nog (DS9: "Behind the Lines")
The title of acting captain was bestowed upon a starship crew member placed in temporary command in the event the normal commanding officer was incapacitated or otherwise unavailable. The line of succession normally started with the first officer and continued to the second officer, and on down until somebody was fit to command.
In an alternate 2371, Lieutenant Veronica Stadi was made acting captain of USS Voyager after Captain Kathryn Janeway was killed during the transit to the Delta Quadrant. (The Mysterious Case of Neelix's Lungs: "Caretaker")
In 2407, Lieutenant (JG) Kanril Eleya advanced to acting captain of USS Kagoshima after most of the ship's senior staff were killed by a hit to the bridge and the chief engineer Lieutenant Hayes otherwise incapacitated. (Bait and Switch: "From Bajor to the Black, Part II")