Lt. Nyota Uhura was the communications officer on the original Enterprise in the first series of Star Trek, and went on to reprise her role in several subsequent films. However, an answer in this question states that she once also held the rank of Captain. When did this happen, and under what circumstances? Futhermore, did it have any lasting impact? I am aware that Uhura's presence as an officer on the Enterprise was already groundbreaking, given the social situation in the United States at the time.
Ep.4 of The Animated Series has Uhura taking command after all the male crew get seduced by the latest planet's ladies.
My understanding is that naval traditional would hold that during that time she was "Captain of the ship". But she didn't change her insignia or claim the rank of Captain.
As Valorum said, I do not believe this ever happened in canon. However, there is an unofficial miniseries in whic Uhura was at least a captain, though perhaps not of the Enterprise:
Star Trek: Of Gods and Men
This is a non-canon miniseries, but contains many of the actors from TOS, including, crucially, Nichelle Nichols. From a transcript:
"Captain Uhura. Welcome aboard. Do you like the ship?"
According to the film's website:
Captain Nyota Uhura has been serving as Director of Starfleet Linguistics, a post she finds extremely interesting, though she feels there may be something missing in her life.
Here's Uhura in her Captain's uniform:
She takes command of the Enterprise in the Animated Series s1e4, where all men of the Enterprise are victimised by beautiful women who stay immortal by draining the lifeforce of men.
It's called The Lorelei Signal.