The Philadelphia-class was a type of survey ship starship which was in service to the Federation Starfleet in the 23rd century. This class was named for the city of Philadelphia on Earth. In 2269, the USS Billy Bishop, a Philadelphia-class vessel, was assigned to patrol the border of the Klingon Neutral Zone. (TOS video game: Judgment Rites) Presumably, there would have been a USS Philadelphia prototype after which this class would have been named, a predecessor in the name to the later starships USS Philadelphia.