One more in a sporadic series.
As long as there have been serious shoot-em-ups in science fiction there have been space navies. The analogy is traditional and 'natural,' and even in the rocketpunk era it easily turned back occasional efforts to model the Space Force after the Air Force. Unlike aircraft missions, space missions take days or weeks, often months, not infrequently years. Crews live aboard their vehicles, unlike aircrews or tank crews.
The naval analogy also invites some ways of thinking about force deployments and space operations. In spite of Star Wars and Battlestar Galactica, there is some preference for drawing inspiration from the big-gun era, especially – and a bit steampunkishly – the Mahanian golden age a century ago, before the World Wars and the complications introduced by submarines and aircraft. In this schema there are broadly three warship types, with familiar and evocative names: battleships, cruisers, and corvettes.
Battleships fight other battleships, especially in fleet actions. They carry the heaviest practical armament and protection, sacrificing some speed and range in order to do so. Cruisers patrol the seaways/spaceways, often operating independently. Though no match for battleships they are formidable against anything else, and are tailored for speed and range: In the classic formulation the ideal cruiser can outrun anything it can't defeat. Corvettes, though to 'Murricans their name connotes a classic car, are lighter patrol craft and workhorses of the fleet, with the virtue of being cheap and therefore plentiful. In the late 19th century these were called gunboats, hence 'gunboat diplomacy.'
Turn the time-regress dial back from 1890 to 1790 and the first two classes become ships of the line and frigates. Corvettes are still corvettes, unless they are sloops of war, gun-brigs, or whatever have you. (Gunboats were then small vessels, often oared, with one or two heavy guns, used mainly for inshore defense.) Ships of the line are rarely seen in space, but the name 'frigate' has captured the popular imagination, and indeed is used by present-day navies.
Take another ride on the wayback machine, to around 1400 – or 400 BC – and the battleships and cruisers blur together. Galleys could be assigned more rowers for cruiser missions, or more fighting men on deck for battlefleet service. (Lesser patrol craft went by a wide variety of names, of which one, fregata, turned out to have a big future ahead of it.) The mission configurability of galleys by loadout is a hint that the three main types are not a universal law, but science fiction has drawn few analogies from the mere 2000+ years of galley warfare.
In SF some hybrid models are also popular – notoriously battlecruisers, cruiser types scaled up to battleship dimensions: dashing, powerful, and with a nasty reputation for blowing up. In space wargames there's also some popularity to using 'dreadnought' for a super battleship, rather than what dreadnoughts were historically, battleships of a later type; and perhaps even bigger classes with colorful names like Annihilator. Destroyers are also rather popular, including as major combatants, though they originated as a specialized type, 'torpedo-boat destroyers.'
Such is the quasi-standard typology. I've used it myself, which didn't keep me from making snide comments about most of these classes here. A number of people have noted that some of these assumptions, such as cruisers being 'faster' than battleships, don't translate very well into space. As practically always, your go-to source is the Atomic Rockets site, specifically here.
But. Space is not really an ocean, and space war forces aren't navies. A few things to think about:
Even without demimagical high level AI, robotics and remote systems will surely be pervasive in space, as they already are. Robotic systems are cheap compared to the cost of spacecraft, they don't require heavy and expensive life support, and no letters saying 'We deeply regret' need to be sent to their families. Human presence, by and large, will be reserved for functions that cannot readily be automated, such as high level decisions – especially Open Fire! and Cease Firing!
Even within the traditional schema, this suggests odd consequences. A corvette has more need of a human crew than a battleship does. A squadron of battleships blazing away at their enemy counterparts in open space does not really call for a lot of high-level decision making, just intensive number crunching. Exercising gunboat diplomacy, on the other hand, or ordering a suspicious spacecraft to stand by for boarding and inspection, calls for policy judgment.
And suppose for a moment that kinetic weapons are dominant. This evokes an image of 'missile ships,' but is that really how it plays out? Say that an enemy war force (of whatever composition) is on orbit from Mars to Ceres, and Earth wants to send a force to intercept it. This does not call for missile ships, it calls for missiles. By definition you don't expect to recover kinetic weapons; their whole purpose is to smash into their target. Expendable buses can use all their propellant for a fast intercept, and use their own mass for whacking the enemy. If you need some battle managers closer than light minutes away, send a control craft along behind them, perhaps fitted with defensive – but not offensive – armament.
If beam weapons are dominant the picture is slightly more classical, but only slightly. Laser platforms don't cannonball themselves into the enemy, and since they are expensive and (unless wrecked) reusable, you would like to recover them if you can. But there is still no inherent reason to put a crew aboard one. It zaps, and is zapped back. The prospects of repairing it in the heat of battle are iffy, or more than iffy, and the repair crew with its life support is an additional expense and vulnerability.
Repairs after battle are more plausible, and for extended missions you might well want maintenance techs as well as a command staff, plus supplies, workshops, and other logistic facilities. But the spacecraft needed to carry all this are more like transport auxiliaries than men-of-war. They might also be largely modular, more like trains than ships. For that matter, fit a military space station with drive engine and tankage and you have a mobile support base. If you win, it becomes an orbital base supporting your forces around the objective. What it never becomes is a 'battleship,' or anything that fits the familiar warship typology.
It isn't even a Death Star, because while it may carry defensive armament there is no particular reason to mount a huge weapon laser aboard it, and good reason not to. If you scale the whole thing down for long range patrol you might call it a cruiser, but really it resembles a cruiser not much more than raiding cavalry does.
Thus, in broad (and sketchy) outline we have a picture of space forces that has little in common with traditional naval fleets. The largest spacecraft, perhaps, are mobile military stations with command and logistic facilities and personnel, not intended for direct fighting. They control and support weapon platforms, some of which might be quite big, whether these are laser platform or kinetic killer buses. You probably also have remote sensor platforms. And you no doubt have patrol/inspection craft, manned and fairly small, to put boots in the airlock when called for.
Taken as a whole you might call it a fleet. But it more nearly resembles a mobile, distributed, and networked fortification, deploying in action into a three-dimensional array of weapon emplacements, observation posts, and patrol details, all backed up by a command and logistics center. (Armies in SPAAACE !!!) Very little of it fits our template of 'space warships,' because it is designed for space, not simply borrowed from the sea.
Okay, your turn. You may fire when ready.
Related links: Part I and Part II of this series. And I took on the unglamorous little detail of logistics here.
Image source page.