Below is a list of military ships with largest to smallest. Please note, there might be some cultural differences. While this list does not detail actual size, crew, speed, etc, this is so variable that it would be ludicrous to assign a value.
Deathstar – iconic. Planet sized warship. That’s no moon. . . . If this is not familiar to you then I would recommend you rethink your military SF writing career.
Planetoid – A small planetoid that has been mined out and covered with sensors, weapons emplacements, etc. Likely has a very low speed, is cheaper than other large ships and can take a lot of damage. Asteroids can also be used to make planetoid type ships.
Battlestar – Very big, like a small city. Also acts as a carrier.
Super Dreadnought – Bigger and badder than a dreadnought because hey, mine is bigger than yours.
Super Carrier – a large platform for smaller fighter craft, because hey, mine is bigger than yours and I have more fighters.
Dreadnought – Big, mean, heavily armored and armed. Usually very slow but very hard to kill.
Carrier – a platform for smaller fighter craft
Battleship – Heavily armed and armored. Very tough.
Hospital Ship – a floating hospital can be used to provide medical support to military or civilians. Hospital ships are generally unarmed.
Light Carrier – a platform for smaller fighter craft. Doesn’t carry as much as a regular carrier.
Battlecruiser – where speed and firepower are more important that armor.
Pocket Battleship – Not as big and as expensive as a battleship. Size doesn’t always matter.
Heavy Cruiser – A heavy, multi-use warship that can operate alone or as part of a formation.
Light Cruiser -A light, multi-use warship that can operate alone or as part of a formation.
Destroyer – a fast, maneuverable, high endurance warship usually intended to escort larger vessels in a fleet, convoy or battle group and is designed to protect against small, faster attackers.
Frigate – Frequently they have many roles. Designed for speed and maneuverability they are used much like Destroyers for protecting against smaller faster attackers. They can also be used as scouts and patrol vessels in dangerous areas. They may support but they do not usually stand in the line of battle with capital ships.
Corvette – This is traditionally the smallest ‘proper’ warship. They can act as couriers, dispatch boats, patrol boats, etc. They can also be used to find stealthed vessels, mine sweepers, etc. Usually the biggest advantage of a corvette is the cost.
Sloop-of-war – Even smaller than the corvette this is not generally considered a ‘proper’ warship and fills the category between dedicated patrol boat and corvette.
Cutter – On par with a Patrol boat they are usually small and used for patrolling close to bases or civilized areas.
Patrol Boat – Generally very short of everything that makes it dangerous the patrol boat can usually fight off mostly unarmed ships but is mostly used to patrol areas that are not dangerous to rate a heavier vessel.
GunBoat – A short range craft with weapons. Primarily designed to attack larger targets in groups, but not as vulnerable as smaller fighters.
Fast Attack craft – smaller fighters or crafts with a small crew these are generally very small, fast and well armed, but lack armor and endurance. They are usually carried on carriers or based somewhere providing close support.
Non Military Ships
Fleet Maintenance Vessel
Fleet Repair Ship
Unclassified Military Ships
Arsenal Ships – missile platform
LAC – Light Attack Craft
LAC Carrier – Carries light attack craft. This may be fighters, gunboats, etc.
Q-Ship – This is built to look like a slow, plodding and usually unarmed freighter but is designed with hidden weapons to lure pirates or raiders in close where they can be destroyed.
Cutter – Smaller transport or patrol ship)
Pinnance – Larger transport, or a ship’s shuttle
Shuttle – Intra system travel or ship to station/ground
Sting Ship – fighter/shuttle escort used mostly to keep up with and escort shuttles or pinnances.
Monitor – Not designed for speed. Designed to watch and with enough fire power to discourage.
Ship of the Wall – This is a Science Fiction Term more closely associated with the Honorverse series. This is more appropriate in a Science Fiction setting since space is more three dimensional and a ‘line’ is so easily destroyed.
Ship of the Line – These are predominantly heavier ships that formed a battle line and dates back to ocean going navies that would line up and slug it out.