Warship Nomenclature And Evolution

Introduction

The naming of ships in science fiction is based on modern naval tradition, which is based of course on historical traditions. I read a lot of military science fiction, especially David Weber's excellent "Honor Harrington" series, which is HEAVILY based on traditions from the British Royal Navy during the Age of Sail. And so a lot of my views are based on that and other science fiction sources like the Traveller RPG.

Ship Classes

Here are some typical classes and what their descriptions and duties are.
Corvette- a small, fast escort and patrol vessel.
Frigate- a small escort vessel, usually larger than a Corvette.
Destroyer- a medium sized escort vessel. Groups of destroyers are sometimes used as scouts or hunting packs.
Cruiser- a medium sized warship, used either as an escort for larger vessels, a flag ship for groups of smaller vessels or as independent, long range raiders.
Battlecruiser- a large warship, usually with the speed and armor of a cruiser but the weapons of a battleship.
Battleship- a large warship, with heavy weapons and armor, but not very fast.
Dreadnought- a very large warship, with very heavy armor and weapons.
Battlecruisers, Battleships and Dreadnoughts are referred to as Capital ships.

Ship Names

The ships of a particular class are usually given similar names to identify them. Ship names are usually historical references, places (especially battles) or words with military references (Retaliation, Courageous, Honor). The British navy had many classes of warships whose classes were referred to as and named for a single letter. So there were "E" class destroyers with names like Echo, Eclipse, Escort and Escapade. Looking at the original Star Trek TV show, the Enterprise and her sister ships Lexington, Constitution, Yorktown, are named for American warships. And the original Lexington and Yorktown were named for Revolutionary War battles. The first ship of a new class carries the class name, so the Constitution was the first ship built and the Enterprise, Lexington, etc are referred to as "Constitution" class ships.
Now for ships in my Serenity game, there's the Glory, a Triumph class cruiser, and their sisters Honor and Victory. The Cortez class includes the Alexander and Genghis. Commander Hwan Fei captains the Peregrine, which is a Frigate class.
Doesn't "frigate'' refer to a ship type? Normally it does, which is a funny story. I had already chosen Peregrine for the specific ship's name, but didn't want to have a class name of Hawk, Eagle or Falcon. I mentioned this issue to my players during the game where they met Hwan Fei. Emily came back with the word frigate, which is a type of hunting seabird, and she thought that would be a rarely used term and would suit my needs. So, I had to explain the history of the naval usage of frigate for a ship type, and that it was a common term in naval parlance. But, since there are no classes of ships in my Serenity 'Verse referred to as frigates, I honored Emily's input and used it as the class name for those ships. And, coming back to the term frigate, in the Age of Sail, a frigate was as large as a ship of the line, but faster and lighter armed, sort of a battlecruiser type. Over the centuries, frigate came to mean a fast and small vessel.

Ship Evolution and Sizes

In general, as time goes by, ships become bigger and bigger as navies compete with their opponents. For example, World War II U.S. Navy destroyers were around 2,000 tons, modern destroyers are around 8,000. Aircraft carriers went from 30,000 to 90,000 tons. And so it is in my Serenity 'Verse. When I was designing the Glory, I wanted something big enough to be imposing to the players' Osprey, but small enough so that the skeleton crew transported on the player characters' ship would seem believable to be able to fly her away.
But now, at least 13 years after she was comissioned, the Glory is the same tonnage as the Operative's Cortez class corvette and a fraction of the size of a Longbow class cruiser. The growth of the Alliance navy ships is not driven by competition with other fleets, but by other factors influencing the Alliance military.
In the Firefly TV show, the massive "joined skyscraper" like ships are referred to as cruisers, the Tohoko class. A cruiser usually means a warship capable of long range independent trips or "cruises". Looking at their stats, they are properly described in the RPG basic book as mobile bases. They are being withdrawn from service and scrapped, replaced by the Crete class carriers, one of which we saw in the Serenity movie at the Battle of Dante against the reavers.

Prewar tonnages were roughly:
Battleships 100-120 ktons
Battlecruisers 60-80 ktons
Cruisers 50 ktons
Light Cruisers 30 ktons
Destroyers 10-20 ktons
Corvettes 5-10 ktons
Patrol Ships 1-3 ktons

EDIT The US Navy is commissioning the new Zumwalt class destroyer which is 14,000 tons. Making her 75% larger than an original model Arleigh Burke class destroyer and 40% larger than a Ticonderoga class CRUISER. In fact, she is larger than most post WWII US cruiser classes.