Acting captain
The position of acting captain was bestowed upon an officer or another individual aboard a starship when the ship's regular commanding officer was unable to command for an extended period of time. The first person eligible was generally the first officer, with the line continuing down the ranks until someone was both physically and psychologically able to command.

History

22nd century
In 2151, when Captain Jonathan Archer lost consciousness after a fight between the  and Sarin's group of renegade Suliban, T'Pol became the acting  of . ()

In 2152, when Captain Archer was on a classified mission with T'Pol,  was the acting captain of Enterprise. ()

Later that year, Paul Mayweather, temporary captain of the , joked with his brother Travis Mayweather, citing that "An ensign ought to salute before addressing a captain." Ensign Mayweather laughed it off, reminding him that he was only that "acting captain" and not to "let it go to your head." ()

In 2154, when Captain Archer became obsessed with protecting a Xindi-Insectoid hatchery due to a chemical from the hatchery's eggs, Trip Tucker led a mutiny in order to bring Captain Archer back to Enterprise so that they would be able to continue their mission to stop the Xindi from destroying Earth. During the time that Archer was recovering, T'Pol was the acting captain of the Enterprise. ()

23rd century
After the capture of Captain Christopher Pike and Number One by the Talosians in 2254, Spock became the acting captain of the . ()

In 2256, Commander Saru became acting captain of the  after Captain  had been captured by the Klingons. ()

Later on, after the Discovery jumped into a parallel universe, Commander Saru again became acting captain of the ship due to Captain Lorca leaving to act on his plan to be brought before . () The crew was ultimately faced with the revelation that the Lorca they knew had been from the mirror universe all along, leaving Saru as acting captain indefinitely. ().

Saru again became acting captain of the Discovery at the conclusion of the Federation-Klingon War of 2256-57, and was in command when the Discovery left Earth for  to pick up Discoverys new permanent captain. () 

In 2266, with Captain James T. Kirk being detained by the staff on Tantalus V, Spock was the acting captain of the Enterprise and referred to himself as such in the ship's log. ()

24th century
While under the influence of the polywater intoxication, Wesley Crusher deemed himself "acting captain" of the  in 2364 after commandeering the ship from engineering. ()

Lieutenant Commander Data became acting captain of the Enterprise in 2367 when Captain Picard was incapacitated due to a lack of REM sleep. () 

Three years later, Data again became acting captain when both Captain Picard and Commander Riker were held captive by Arctus Baran. () 

On several occasions from 2372 until 2375, Lieutenant Commanders Worf and Jadzia Dax were made acting captain of the  for missions in the Gamma Quadrant and during the Dominion War. Captain Benjamin Sisko was the commander of Deep Space 9, which during the war was the headquarters for the Federation Alliance, and would often demand his close attention. As such he would entrust to his most senior Starfleet officers command of the ship and its crew. ()

Several members of Red Squad were promoted to acting officers. ()

Aboard the Silver Blood , its copy of Ensign Harry Kim assumed command of the starship as the highest ranking surviving officer, after his own senior officers had dissolved. ()

In 2399, William Riker identified himself as acting captain of the  after briefly returning to active service to help Admiral Jean-Luc Picard against the Romulans. ()

Alternate reality
In the alternate reality 2233, Lieutenant Commander , first officer of the , became acting captain of that vessel after Captain Richard Robau was forced to leave the ship and was subsequently killed. Captain , who later wrote a dissertation on the incident noted that Kirk was captain of a starship for a mere twelve minutes but saved the lives of the eight hundred crewmembers aboard the ship. ()

In 2258 in the same reality, Captain Pike of the  appointed Commander  acting captain and George Kirk's son, Lieutenant , as first officer when Pike left the ship to confront Nero. Subsequently, Kirk proved that Spock was unable to perform his duties and then Kirk himself was made acting captain. After everything was over, Kirk was promoted to the rank of captain and given regular command of the ship. ()

Later, in 2259, Kirk placed  in charge when he and other members of his crew flew a K'normian trading ship to Qo'noS to apprehend John Harrison, a move which  questioned, saying, "You just sat that man down at a high-stakes poker game with no cards and told him to bluff." Kirk rebuffed his concerns. ()

As acting captain, Sulu ordered the refueling and preparation of the K'normian ship for Kirk and his team. He also delivered an ultimatum to Harrison that impressed McCoy and caused the doctor to revise his earlier opinion. ()

When Kirk was aboard the  and the Enterprise was falling towards Earth, Spock, in the role of acting captain, ordered the entire crew to evacuate the ship while he remained behind to ensure their safety until they did. Sulu and the rest of the bridge crew declined, strapping themselves in. ()

31st century
In 3189, Saru identified himself as acting captain of the Discovery'' to . ()

Related links 
 Acting captain's log
 Acting captain's starlog, Enterprise (NX-01)
 Acting captain's log, USS Enterprise (NCC-1701-D)
 Acting captain's log, USS Voyager
 Acting captain's personal log
Titles