I'm toying about with space opera, and I'm thinking about to type ships. Any organization of ships must make reasonable sense to a reader without having to memorize a slew of specialized vocabulary.
For interstellar ships, capable of crossing significant distances, I want a categorization similar to modern naval size usage. They combine fabulous speed with fabulous expense, at the expense of firepower and defense. For non-superluminal ships, I want slightly different, yet still accessible vocabulary, so that readers get a good gut feel for those ships relative to modern naval usage.
Cruiser/Carrier (same size, different specialization)
Intruder (analogous to attack subs and strategic bombers)
Able to cross interstellar distances, attack ships are the backbone of the strategic fleet. Their ability to strike anywhere lends these ships considerable punch, but those advantages require considerable compromise. Superluminal drives are large and prohibitively expensive, and together with the requisite reactors to power them, limit both weaponry and defenses. Attack ships are expensive to build, expensive to maintain, and expensive to repair, but as they are able to protect numerous system, these ships still wind up cheaper than building and manning extensive local fleets.
Over the years, numerous attempts have been made to create a battleship class, but their cost relative to their effectiveness keeps dooming category to obsolescence. Fundamental physics indicates that superluminal drives will never be miniaturized enough to make a battleship class cost effective.
Relatively cheap and able to cross a solar-system a near light speed, ton for ton, local ships deliver more firepower while withstanding considerably more punishment than comparable attack ships. Even obsolete local ships can easily maul an attack fleet. With a support network of satellites, beacons, and buoys, defenders easily have an unparalleled view of the battlefield. Despite these advantages, local ships are only useful when they are deployed to the correct locations. Meanwhile, redeploying these fleets with Heavy Ferries takes considerable time, meaning that attack fleets tend to pick battlefields to their own advantage.
The primary goal of local defenses is to discourage attacks while increasing the forces committed to any attack.
The most common local ship is the cutter. Cheap, reliable, and flexible, these ships take on patrol and policing duties in almost every settled system. Busier and more important systems usually have several corvettes.
Monitors and gunboats are predominantly used in sieges, as temporary command centers, and as bulwarks when local fleets need reinforcement. They are transported by heavy ferries.
A ferry is a specialized carrier that transports capital ships from one location to another. While smaller ferries are fairly common, heavy ferries are rare due to their staggering cost, needing engines able to move gunboats and monitors between systems. While all ferries are prized targets, heavy ferries are to be destroyed at all cost.
Ferries sometimes work with attack fleets, transporting local ships to bolster the attack force's resilience, especially in assaults against bases and planets. The attack fleet secures an area while ferries bring in the heavier firepower.
Bases and space stations, completely freed of any drive requirements, pose yet another challenge. These constructs can withstand considerable firepower while inflicting overwhelming damage. Even a small, relatively cheap base poses a legitimate challenge to the largest superluminal ship.