The Romulan heavy and strike warbirds were the equivalent of heavy warships. (Ship Recognition Manual, Volume 5: Starships of the Romulan Star Empire)
The organization of the Federation called the United Federation Starfleet, or simply the UFS—was a new reorganization of the entire Federation as it brought all the planets within the Federation together as a more united empire.
The United Federation Starfleet, or the UFS
The beginning of the 29th century was a time for the Federation Starfleet to reorganize itself into a more cohesive power and leader for the galaxy. It was at this point that the Federation Council decided to unite the planets and it's allies into a more united organization. The name they chose was UFS, or the United Federation Starfleet.
Heavy warship classes