The captain of the Royal Navy's warship, HMS Queen Elizabeth, has been removed from his command following reports that he misused an MoD car.
The Royal Navy confirmed Commodore Nick Cooke-Priest had been reassigned to a new role, without giving a reason.
But navy sources told the BBC that his removal was over his use of an official car for personal trips.
A new commanding officer has been appointed to the £3bn aircraft carrier.
The BBC's defence correspondent Jonathan Beale said that "while the offence may appear relatively minor, it was felt that his position had become untenable and that the commanding officer must be beyond reproach".
"It is not the end of Cdre Cooke-Priest's naval career but it is a black mark and a humiliation to lose the command of Britain's largest and most expensive warship," our correspondent added.
Anyone who has use of an MoD vehicle can only use it for official business, with each mile needing to be recorded.
A Royal Navy spokesman said: "We can confirm Captain Nick Cooke-Priest has been reassigned to a new role.
"We can only say that management action is ongoing and it would therefore be inappropriate to comment further."
Cdre Cooke-Priest, who joined the Royal Navy in 1990, had been in command of HMS Queen Elizabeth since October.