The USS Allegheny was a Federation starship, a Galaxy-class explorer in Starfleet service in the 24th century. By the 2370s decade, the Allegheny was under the command of Captain Namura and the flagship of the Third Fleet.
On stardate 54637.3, in the year 2377, the Allegheny led the Third Fleet into the Delta Quadrant as part of the Starfleet offensive against the Borg Collective. While travelling through System J-356, the fleet was ambushed by unknown vessels. At the conclusion of the battle only the Allegheny survived and managed to send a distress call to the USS Enterprise-E. Captain Namura later identified the unknown vessels as belonging to Species 8472. (ST video game: Armada II mission: "The Cavalry")