In a future space navy universe that is heavily based on modern wet navies, would it be acceptable for a vessel XO (rank of Commander) to be field promoted to Captain from a single Fleet Admiral?
To add more context: the former captain is being removed from duty and placed under arrest for a major crime he committed. The XO had been investigating this and brought the information to an admiral. The XO has been an XO for about 4 years at this point, 2.5 of which has been on the current ship with the same captain. He is a highly decorated and admired officer among both the enlisted and the Admiralty.
I know field promotions tend to only happen in times of war, but the current world environment is a cold war era vibe.
More context: The star system is the Alpha Centauri system and the main navy is from the Republic around aCenA. The ship is essentially a flag ship as it is one of the most powerful cruisers that does long-duration solo missions on the outskirts of the Republic space that boarders the B-star space.
The XO was initially selected to command the ship but was rejected command because he was not a captain and still too young/inexperienced in some of the admirals eyes. He has since been the XO for 2.5 years, a few months of which he was acting captain as the main captain was on private leave (rebuilding his drug ring and saving his sons life because that is why he is in the drug ring to begin with). Basically there are a few admirals who want him to be the captain and some that don't.
While the 2 star systems (A and B) are not at war, there are several proxy wars going on and heightened tensions with several close-call events that could spark the inevitable war.
The Captains crime also link back to the murder of several crew members and other people outside of the ship.
Final Decision: Thank you everyone! Based on the input, I think it will be that the XO simply takes on the role of Acting Captain. The admiral could add something like once the ship makes port or at next leave he will be in for a promotion and a new XO for "his ship".