Men O'War -Vessel Classes

The smallest standard warship class is the Corvette, also known as the patrol ship. Corvettes are usually no more than four to five hundred thousand cubic feet in size. They have a small crew and are used for custom and policing duties, by both the Legion and Rangers. Other space navies use them for equivalent duties. Corvettes are lightly armed and armored.
The Pinnace is an even smaller vessel. Typically between 250 thousand and 400 thousand cubic feet, pinnaces, though they have hypershunting capability, are typically carried aboard other vessels to provide couriers, engage in scouting tasks and provide messenger services. A Pinnace is typically an armed vessel. They are capable of landing on world, which larger combat ships are not, as well as operating in hyperspace.
The Schooner is a lightly armed, swift courier vessel which often accompanies fleets and tasks forces. Like the Pinnace they are small enough to be embarked on major combatants as auxiliary vessels. most Schooners are in the fifty thousand to hundred thousand cubic foot range.
Frigates are more heavily armed ships designed for independent duty. The typical frigate is from 5 to 8 million cubic feet in size, though some Midland forces are known to field frigates in the ten million cubic foot size. Frigates range from medium to heavily armored and are usually outfitted to provide for planetary combat support as well as space combat. This means they embark a number of space and planetary combat craft, as well as having sufficient personnel to man them.
The Destroyer and its even smaller cousin the Destroyer Escort are ships in the 5 to 6 million and 3 to 5 million cubic feet range respectively. Unlike the Frigate, Destroyers and Escorts are designed to provide support to larger warships or convoys of merchant craft. They are neither designed for independent action, nor capable of supporting planetary combat.
A Battlerider is a small vessel in the 50 thousand to 400 thousand range optimized for space combat. Unlike the Pinnace they lack passenger facilities and though shunt capable and landing rated, they are seldom used for any other purpose than space combat. Most battleriders are specialized with a specific weapons mix or sensor package. They most often operate in groups which consists of craft of varied capabilities.  Like most large space combatants they are typically roughly spherically shaped.
A third-rater or Battleship is a ship of the line usually in the 10 million to 50 million cubic foot range. Battleships are the lightest of the ships of the line. They are armored with heavy force fields. Like all ships-of-the-line a battleship will have a large troop contingent, as well as combat support craft, including many battelriders.
A second-rater or Dreadnought is a ship of the line usually in the 100 to 200 million cubic foot range.
A first-rater or Superdreadnought is a ship of the line usually in the 200 to 250 million cubic foot range.