Space warfare is totally different from anything people have experienced or developed in history on Earth. The extreme conditions of the universe dictate completely different demands on ships and fleets. Dogfights or submarines have no place in the depths of space, heavily armed capital ships that can perform various roles, dominate the battle theater. In the orbital space of populated planets, there is a need for smaller and more specialized vessels that can perform tasks that battleships are too crude for.
However, the origin of the space fleet in the naval force of the earth can not be denied to this day. Out of this tradition, some terms have been preserved that originally referred to ships of the wet Navy, but their duties and functions differ drastically from these.
The most important types of ships, which can be found in almost all star fleets, are explained here in function and role.
The name „korfette“ comes from 15th/16th century Dutch and refers to a small („-ette“) korf, a then common type of ship.
Modern corvettes are more lightly armored and armed than frigates, while not being as quick or maneuverable. They are usually used for escorting convoys and patrolling orbits, especially in places where larger ships willd be unnecessary. Corvettes can also be used for taking out larger vessels already crippled by other ships, almost making them akin to scavengers. In many ways, corvettes exist just to have a ship or two (or ten) available; being smaller and more lightly armed means that they are cheaper to construct. Many space police forces rely on corvettes for patrol and control tasks. Rarely will they make up a larger part of any warfleet, though.
“Frigate-built” was a term used in the 17th Century describing a warship that was built to be quick and maneuverable.
In modern times they are smaller vessels with light armament and armor (but more powerful and larger than a corvette), suited for speed and maneuverability. They often act as patrol and escort vessels, whether for a merchant convoy, a single capital ship, or a fleet. Their agility and maneuverability means they can move to redeploy and protect other ships better than larger, slower moving vessels. It’s likely to see a strength-in-numbers strategy with them. They are not considered capital ships and not built for elongated deep space missions.
Destroyers existed for a short period of time in Earths navies. Their main role was to fight submarines.
Unlike their historical predecessors, these ships are not designed to combat disguised ships (there is no camouflage in space), but specialize in escorting invasion fleets. They protect dropships and troop transports and can be used as bombers against orbital installations and planetary surfaces. They can be more specific and accurate than large battleships, which have more firepower, but cause great collateral damage when they target them against planets. Destroyers will almost never act on their own but only as part of larger fleets.
In the Age of Sail “cruiser” was a term used to describe ships which underwent “cruising missions;” that is independent scouting, raiding, and commerce protection missions.
Cruisers now are medium-sized vessels, able to operate independently but also commonly seen within a fleet. They would have the capacity to be used as anti-fighters, planetary bombers, raiders of enemy supply lines, and scouts. However, they would also be the type of ship most likely to engage in non-combat roles such as exploration or even colonization due to their ability to operate independently for extended periods. I would not expect cruisers to commonly be used in front-line assaults of an enemy fleet; that role is better left to other ships. However, they have the firepower, size, and better defensive capability to go up against other ships when needed and it’s not uncommon to see cruisers making up the bulk of fleets in some settings. They are a jack of all trades but in no role do they stand out. For many tasks, it is actually better to use a battleship or a smaller ship. Therefore, many cruiser designs are also found in the civil sector, in police operations or for trading purposes.
A cruiser turned into a troop carrier. Their job is to transport ground based combat power to target worlds and deliver them with organic interface craft. They may carry interface fighters and strike craft as well as landers, they may even have their own space to surface weaponry for fire support, but most of their displacement is given over to housing troops, their vehicles, their gear, and their supplies.
Battlecruisers (or battle cruisers) are the first vessels in this list to commonly be considered capital ships. Battlecruisers and battleships, thus, often act as the heavy hitters in a fleet; they are the main combatants and are protected by other vessels such as frigates and destroyers. Battlecruisers are not as versatile as Cruisers and not as powerful as Battleships. The mix of those two classes offers interesting support roles in large scale battles, though. Battlecruisers are the largest ships you will normally see in a conflict near a planet.
Battleships are different from Battlecruisers as they lack the ability to operate entirely on their own for extended periods. They are built to be part of a larger force or stay in a very small theater. They trade movability and range for more firepower, though. The slowest form of a Battleship is a Weapon Platform, usually installed in near orbit or at crucial points in space (like transit points). Some Battleships are used for very specialized roles like Fleet Control or Command Ships.
Carriers tend to be some of the largest capital ships around due to the need to hold and transport large numbers of fighters, bombers, and other craft. Typically, though not always, their hull-mounted armaments are light; carriers usually rely on the large numbers of fighters they carry (when operating solo) or their fleet for defense and attack of other ships. The ability to carry craft does not make a ship a carrier by default; many frigates and cruisers, for example, will carry a complement of fighters or a few ground vehicles. In order to be considered a true carrier the vessel’s main role needs to be the transport and deployment of smaller craft.
Historically dreadnoughts are especially large or heavy battleships. The term is quite fantastic and was meant to inspire awe and fear. Dreadnoughts are just about always gigantic ships; massive vessels that dwarf even the largest battleships or battlecruisers. The role they fulfill is exactly like a battleship or battlecruiser; complete dominance and superiority. Intimidation, even more so than with battleships, is the name of the game when it comes to dreadnoughts. Due to their large size they can often carry a large number of secondary craft, like a carrier. Often enough, dreadnoughts can carry more secondary craft than any carrier (altough super-carriers exist).
The Tanker carries reserves of propellant and reactor fuel to replenish the fleet. Since propulsion within a system is by reaction drive, massive quantities of reaction mass get consumed, and it is the Tanker’s job to keep the fleet fueled. Tankers usually carry harvesting craft to find sources of hydrogen, deuterium, and helium-3 and have their own processing plants to turn raw materials harvested into useable propellants/reactants. An army marches on its stomach, and so too a fleet maneuvers on what is in its tankers.
Logistics Ship (AOE)
A military version of a freighter, usually identical to existing civilian merchant classes, with perhaps a slight upgrade to armament, communications, and protection. Warships need spare parts, replacement missiles and other expendable stores, water, and food.
Tender Ship (AGL)
A repair ship. These carry fabrication plants, raw materials, and technical shops to maintain, repair, and in some cases even rebuild parts of spacecraft to keep the fleet in the fight away from their home stations.