Battleship
In the days of wooden sailing ships, a “ship of line” was one that was meant to go toe to toe with the big boys and come out in (mostly) one piece. They were ships that were meant to fight other ships. Hence the transition to the term “battleship.” Modern battleships, at least in U.S. Navy policy, are meant for shore bombardment.
In Hasbro's old game, the phrase “You sunk my battleship!” was intended to be spoken with feeling, and there's a reason for that. No battleship in Star General goes for under 220 RPs. Unless damaged, they can reliably destroy anything except another battleship (and possibly a battle cruiser) in one round, and it is virtually impossible to bring one down without losing at least one ship.
If you can bring a battleship into orbit of an enemy world, you're sure to discover their other function; the 500-RP-a-shot neutronium bomb destroys whatever it hits on a planet, as well as anything within one hex of the impact point. Choose your targets carefully—your battleship's guns can fire as many of these as you have the cash for, but they come from the purchase panel, so you only get them in the first ground turn.
Hressan battleships have a clear advantage in unrefueled travel range, while the Khalians' Weasel 1 carries the most ammo.
Cruiser
The ultimate general purpose warship. Cruisers obviously don't pack the wallop of a battleship, but they're faster and a lot cheaper. They are best used for punching your way through escorts so you can get at that capital ship, and for stopping the enemy's heavier guns from reaching your own high-value ships.
The Khalian Minx-class cruiser leads the pack: it has the firing range of a battleship, and is almost as powerful as a Xritran battle cruiser!
Destroyer
They used to call these “torpedo-boat destroyers,” because until submarines came along, that's what they did. They are quite good at it in Star General too—the crews of lightly armored missile boats know they are in deep doodoo when destroyers show up.
Where battleships rely on a hefty punch of beam firepower, destroyers use a lot of missiles. And remember—beams damage things, missiles smash them. One of the best use for destroyers sounds a little crazy: taking out battleships. In almost every battle, beams are used before missiles, meaning that your poor little destroyer will get chopped to bits by that battleship before it even gets close. But there is a 25% chance that your destroyer can sneak in, and get it's missiles off first. If that happens, the battleship is toast, and your destroyer doesn't get a scratch.
The Hressan navy's destroyers are the fastest of their type, and can travel the farthest without replenishment, while the Cephians have a slight edge in firepower.
Battle Cruiser
Users: Fleet, Xritra
The guns of a battleship; the armor and speed of a cruiser. Sound like fun? It wasn't. The crew of Britain's HMS Hood found out the hard way that speed doesn't help when you are nose to nose in a battle line, facing the kind of fire your ships are designed to dish out, but not take.
But in Star General, a properly employed battle cruiser can reach it's full awesome potential. One of the coolest things to do is to take a group of five or six battle cruisers, set them alongside the enemy's line of reinforcement to a planet you are attacking, and watch them send hordes of “tin-cans” to die helplessly under your beams as your battle cruisers dash in, zap some enemy ships, and dash back to their starting positions.
These ships are also great for resolving those massive line battles; they can just charge in, plow through enemy lines, and hold open the gaping hole they create, long enough for your battleships and cruisers to flank the planet and close it up.
Between the two classes of battle cruisers in the game, the Xrita Spider-A has longer-ranged guns and greater long-term endurance, while the Alliance's Delos-class has superior firepower.
Light Cruiser
Users: Fleet, Hressan, Khalians, Xritra, Dragonians
Sort of a “battle destroyer,” built to carry heavier guns than a destroyer and get them there quicker than an average cruiser. Light cruisers can stand up to beam fire pretty well, and some of them carry missiles. I don't use them at all, but if I did, I would send them on fast raids against soft, high-value targets like tenders and space docks, that the enemy has unwittingly left unprotected.
The Fleet's Marsoplis-class travels the farthest and the fastest of the light cruisers. The Schleinel prefer their heavier Wolf-class cruiser, while the Cephians choose firepower over speed.
Destroyer-Escort
Users: Fleet, Hressan, Khalians, Xritra, Dragonians, Schleinel
It would not be completely inaccurate to call a destroyer-escort a frigate. This is basically a destroyer built around beam firepower and able to soak up missiles better than a capital ship. Use these to hold enemy destroyers at arms length while your cruisers and battle cruisers volley from behind and zap them one by one.
The Schleinel and the Dragonians hold the edge in this category. The Cephians use their destroyers for the same purposes.
Gunboat
Users: Fleet, Hressan, Xritra, Dragonian
Gunboats are basically a poor man's destroyer escort. They're designed for the exact same purpose, and are even faster and better defended against missile attack. Otherwise, they have no real advantages over a DE. Use them if you can't or won't spare the RPs for destroyer escorts.
Missile Boat
Exactly what it says: a giant missile launcher with a bridge and some engines. Missile boats are very effective against destroyers and DEs, and at tech levels 2 and up they can even take out a first-gen cruiser or battle cruiser without suffering any damage. MBs have about enough armor and shielding to withstand bits of space junk, so protect them well.
Monitor
Users: Fleet, Xritra, Dragonian
Not to be confused with the American Civil War ship of the same name. Where a battle cruiser is essentially a battleship with a cruiser's armor, a monitor is the other way around. They are better able to absorb fire than to deliver it, are the slowest thing you can build in the game that can still move, and in the Fleet and Dragonians' case, carry the firepower of a battleship. (The Xritra Widow 1 is armed primarily with missiles.) Pure defense. Keep them near your space docks.
Orbital Station
Users: Fleet, Hressan, Xritra, Dragonian
Orbital stations, as the name implies, have only station keeping thrusters and can't move. They have the gunnery of a cruiser or battleship, and roughly the same armor and shields. I recommend using monitors instead if you have them.
Manned Torpedo
Users: Cephian, Schleinel, Xritra
A kamikaze ship, straight-up. It goes without saying that to use these, your race has to be either seriously cold-hearted pragmatists, or a little crazy. The Schleinel and Xritra are seriously cold-hearted pragmatists, and the Cephians are a little crazy.
Manned torpedoes are horrifically effective. As few as two will vaporize a brand new battleship. The Xritra's are a bit weaker, but feature a neat “splash” effect that causes light to moderate damage to other ships within one hex of the explosion. Cephian MTs have powerful warheads, but are a bit easier for defenders to pick off. The Schleinel have the deadliest MTs, with superior range and firepower to the other two users.
Tender
Remember our poor destroyer whose radar got trashed? As a warship, all her storage is quite sensibly allocated to fuel and ordinance—she couldn't carry a spare radar. Well, a tender can.
Tenders can replace the things your damage control teams can't fix. Their physical protection is quite well-balanced: destroyer-level beam shields and cruiser-level armor. Nevertheless, don't leave them unprotected. Your tenders should remain safely behind your lines during the battle, and emerge to do their thing after the dust clears.
Contrary to what you might think, tenders are not unarmed; they usually have a few small beam cannons for stopping micrometeorites, and the Cephian and Xritra versions even have missile launchers!
Transport
Space is big. For your troops to get where they are going, they need a ride. Transports are thin-skinned and lightly armed, but seeing as you literally can't win the game without them, they are not the “queens” of the space-battle chess board; they are the kings. Lose them, and you lose that battle.
In addition to its big Matilda-class, the Fleet has a smaller, cheaper transport with more speed and a missile launcher. I've never used a “Spee”, but I suppose they might be good for getting ground reinforcements to important places in a hurry.
The Khalians top the category in ammo yet again, while the Xritra Spinner-1 stands out in carrying capacity but is very weak in every other stat.
Transports have “look-down” radar that allows you to see what is on an enemy planet's surface.
Recon
The importance of these ships has already been discussed, but cannot be overstated. Recons are your eyes. Try to defend without them, and you will suffer massive casualties even if you succeed in driving the enemy back. Try to attack without them, and you'll end up moving your ships around aimlessly, trying to counter every new defensive hurdle as you discover it and watching the death toll mount as your attack force melts away.
Recons can see farther than many ships can travel in a single turn, are as fast as a destroyer, and have the biggest possible fuel load. Hressan and Xritra recons carry missiles, while the Fleet's have best missile defenses.
The presence of a recon in orbit of an enemy planet will allow you to get a look at the surface.
Sub-ether
In my opinion, this is kind of a stupid-sounding name, but the concept of a using a warp field as a cloaking device, which is pretty much how the manual describes it, is interesting. I don't see the stealth aspect of sub-ether ships being very useful against the game's AI, but the Cephian Silent Dagger ought to be a transport's worst nightmare in on-line games. The Fleet's Kepper Jack is pretty clearly meant as a stealth recon.