If the past is any guide, in the future there will still be war. And if the future involves spaceships, these will be adapted appropriately.
Now, according to the cannon of Space Opera, space fleets should be classified by analogy with 20th century Old Earth navies. Far be it for me to challenge this popular and venerable trope, as universal as cantinas and bounty hunters, mining asteroids and penal planets, alien artifacts and derelict spaceship junkyards. I give you therefore the Space Navy.
The following warships are listed according to size, from smallest to largest:
Fighter – small, fast, maneouveoureable, heavily armed but lightly armoured or totally unarmored, these short-range atmospheric (conventional aircraft), transatmospheric (Aerospacer), or vacuum-only (Vackfighter) attack craft are basically useless for anything other than very close combat against slow-moving targets. This is because, due to the need for high thrust and multi-G acceleration, their delta V is so limited that they are little more than glorified shuttlecraft. Fighters are only employed by the Military Entertainment Complex against soft and easy targets. The real work is done by Fighter drones, which are small, expendable, reliable, capable of sustaining much greater g-force, and piloted by simple AI alone.
Dropship – as the name indicates, dropships drop troops from orbit, down the planetary well to engage in surface targets. They are not deepspace capable and have no propulsion other than decellereationa nd landing rockets. They are cheap, mass fabricated, unarmed and only lightly armoured, and therefore considered by unfortunate troops in them as something very like flying coffins. Because of the expense of getting back up the gravity well, most dropships are disposable. Indeed, were it not for the Military Entertainment Complex, there would be no reason to use dropships, or ground troops, at all. Generally, only those squadmates on RealPlatoon who have failed their challenges and are nominated for eviction end up in dropships
Gunshuttle heavily armed and armoured short range military vessel carried on larger ships, used for boarding, ground or ship assault, and transport. Fusion powered, with some atmospheric capability, capable for travel between nearby ships and space stations, or orbit and surface of a moon or planet. Short-range only, not interplanetary or hyperjump capable. Generally around 30 to 50 meters in length, around 200 tons in weight.
Fastboat / Fastship – the smallest class of military ship, a small torchship, intermediate between fighter and fleet escort, generally fifty meters or so, and around 300 tons, armed with only light weapons and thin armour, but with a proportionally large fusion pulse drive, giving high delta V and acceleration, used for scouting, reconnaissance, courier, and light patrol work. Generally have a crew of five to ten. Includes cheap non-ftl (fastboat) and expensive ftl (fastship) versions. Some fastships are armed with missiles only (missile boat) or missiles and heavy lasers and used as long-range fighters. Reactor radiation means crews have to be rotated regularly or they wouldn’t last long.
Gunboat the smallest autonomous military ftl ship, with the lightest armament and shielding. Used for showing the flag in backwater hinterworlds, gunboat diplomacy, blockades, patrol. Slower (less acceleration, but good delta V), lightly armed and lacking the performance of a Fleet Escort. Generally in the order of 70 to 90 meters long and around 750-1500 tons.
Fleet Escort – the FEV (for Fleet Escort Vessel) – intermediate between Gunboat and Crusier, used for convoy duties and to provide long range reconnaisance, gunboat diplomacy, fleet escort, and other roles, such as catching missiles meant for the high value targets. Using fusion pulse in-system, and ftl jump-capable, with more powerful weapons and shielding, faster and with longer range, than a Gunboat. Generally in the order of 90 to 100 meters long and around 1500 to 3000 tons.
Cruiser – the mainstay of any fleet, these are large ftl/interstellar warship, often heavily armed and passively and actively armoured, and capable of prolonged operations away from the fleet or port. Generally divided into Light, Medium, Heavy, and Battlecruiser, although the latter is sometimes placed in its own category.
o Light Cruiser – intermediate between fleet escort and cruiser proper, and equivalent to the wet navy destroyer, the light cruiser provides fleet support and escort duties, as a screen around the larger and more high value capital ships. Around 100 to 150 meters long and 3,000 to 6000 tons
o Medium Cruiser – classic multipurpose vessel, often sent in situations where a heavier capital ship not required, usually accompanied by a couple of smaller vessels and a few tenders. Generally in the order of 200 to 250 meters long and 10 to 20,000 tons
o Heavy Cruiser – a formidable warship in its own right, with its own squadrons of drones and fighters, either used as center of its own taskforce or to supplement even larger capital ships. Around 250 to 300 meters long and around 50,000 tons
o Battlecruiser – intermediate between cruiser and dreadnought. The Battlecruiser combines the speed of a cruiser with the firepower of a battlestar but, lacking adequate protection, is always the first to be blown up in any battle. Despite this, this is a popular type with many fleets. Around 350 to 400 meters in length and 100-200,000 tons in weight.
Dreadnaught – very large, powerful, and expensive ftl warship. Also called battleship and battlestars. Generally armed with powerful offensive and defensive weapons, fleets of fighters, and heavy armour Size, from 500 meters in length and 400,000 tons in weight upwards.
Carrier – very large (length 500 meters or more) interstellar military vessel which transports smaller craft (fighters, dropships, fastboats, gunshuttles, etc), as well as drones; relies on escorting smaller ships and its own fighter cloud for protection. Several types, e.g. Assault, Deep Space, Supercarrier, etc
Transport – like a carrier but transports troops and dropships. Ftl capable, poorly armed and armoured, moderate performance, medium to large in size.
Auxiliary Vessels – includes tenders, refeulers, intelligence ships, hospital ships, manufacturing ships, etc. All are ftl capable. None is fast or more than very lightly armed.