Obviously Serenity couldn’t have a chance of conquering even NEBRASKA. Just as obviously, the Death Star could do it over lunch. What others?
Only rule here is that fictional fleets are ineligible. Has to be a single ship.
The royal yacht of the Hroshia known as “Lummox”.
Unless they were bluffing.
Space Battleship Yamato - though, of course, it was used to defend Earth against alien battle fleets.
I wanted to say I disagree, as my thought was we could take it with heavy losses. But then I remembered they obliterated Gamilon.
Poor Yuki Mori.
Assuming we’re talking about Earth as it exists in present-day reality:
- Any of Starfleet’s 24th century heavy cruisers. Certainly any ships of Galaxy class, Intrepid class, Defiant class, and Sovereign class. All of these have demonstrated sufficient firepower to scare our current world leaders into immediate submission, or obliterate us entirely. I’m willing to bet that Constitution class, Miranda class, Excelsior class, and other 23rd century ships could do it too.
-Any heavy cruiser-level ship from any of the other races in Star Trek. Romulan, Klingon, Cardassian, etc. Most definitely a single Borg sphere or cube could do it.
If the task is to defeat Earth it’s easy.
The Enterprise could easily do it. We don’t have anything that can destroy its shields.
The Defiant could certainly do it. Even if the quantum torpedos didn’t do the job they could tractor chunks of iron from the asteroid belt at .25c, and that would ruin any government’s day.
Any Star Destroyer has a compliment of men and attack machinery that could do a nice job.
Any Star Trek vehicle with a shield and a phaser stands a pretty good chance. You might be able to overthrow Earth with a runabout.
Serenity could probably blast Washington DC with its atmospheric burn. But eventually we’d likely get a nuke to detonate close enough to take it down. Then it’s up to River to do it hand-to-hand.
If you need to be able to hold it and establish a base of operations from which to control it, you’d probably need a minimum crew size.
[jackass]
*Enterprise *had no shields. This was made clear in every episodes of all four seasons.
[/jackass]
The Battlestar Galactica could certainly do it. Unless you disqualify that as a “fleet” due to its little viper fighters or whatever they are called.
Nah, I’ll allow those. And if you disqualify Galactica you have to disqualify Voyager as well, as they had an infinite number of shuttlecraft. 
If you had been watching carefully, you’d note that Enterprise has no shields. The Enterprise, as it is known in all other incarnations does.
In any case, the polarized hull plating could defeat nuclear impacts. 
Lexx from the series of the same name:
I seriously doubt it. And even the one true Enterprise had troubles with a nuke once, though admittedly they’d have us on range.
Present-day Earth, anything that routinely travels between planets could do it, even including Serenity. Pick up a chunk of rock, put it in the hold, fly towards Earth at high speed, open the hold doors, change course, repeat. We simply have no defense against an attack like that, nor any weapon that could fight back. As Niven and other SF writers have many times pointed out, there’s no such thing as an unarmed spaceship.
If we’re restricting ourselves to weapons intended for use as weapons, I’ll toss in the Skylark for consideration. A hull as thick as a battleship’s, but made from a material 500 times stronger, and machine guns that fire bullets equivalent to small nukes.
I just don’t believe that Serenity has the fuel reserves to do that more than twice, and I don’t think it’s agile enough to avoid getting shot down in the process.
I agree, that wave motion gun had the power to do it
The Galactica is like an interstellar aircraft carrier. The Galactica had the missles to do the job without the vipers
Fuel might be problematic, depending on how processed they need it to be beforehand (can they land on Europa and crack water into usable fuel, for instance?). But they don’t need to be agile to avoid getting shot down: They’re not dodging fire, they’re just staying out of range.
And even just two shots might be enough, if they bluff well enough (and the crew of Serenity is considerably better at bluffing than at orbital mechanics): Land the first one in the middle of DC, flattening the White House, Capitol, Pentagon, or similar high-profile target. Possibly repeat in Moscow, or Paris, or the like. Promise to repeat with some other high-profile target unless everyone surrenders. Sure, you don’t have the fuel to back up your ultimatum, but does anyone on Earth know that?
remind me never to play poker with you
Getting shot down isn’t an issue; releasing that rock, aimed in the correct general direction, anywhere inside Luna’s orbit will strike the Earth somewhere. And I’m sure that River, at least, could work with the navcomp to aim that rock better, from farther out. We can’t throw anything back at her that she’d need to dodge.
Fuel is another issue. It’s not entirely clear what spaceships in the 'verse use, or where it comes from. They’d probably need some sort of base to fly from–but I’d think that would be true for any ship from any hard SF universe. Since Serenity is sublight, her base would need to be a lot closer than Enterprise’s–but even the Enterprise will run out of gas eventually, and I don’t know where they’d find dilithium crystals around here. (I checked at Home Depot, but no luck.)
My turn: how about the Post-Dated Check Loan from Schlock Mercenary? Or any of the battleplates? (The Serial Peacemaker is probably too small for anti-planet activities.) In non-web literature, I’d bet a LAC or superdreadnought from David Weber’s Honorverse would have a good shot at terrorizing our little globe into submission.
Any Shadow or Vorlon vessel. Any of the ancient races ships. Probably any Whitestar. Possibly any Minbari cruiser. Dunno about the Narn or Centauri ships–they lagged in tech behind the Minbari, I think.
Any of the really big Berserker ships could do it. That’s what they were designed for.
That weird thing that ate Captain Pike–which according to one of the novels, was an anti-borg weapon designed by Guinan’s race, I think…but I was rarely sober the semester I read that instead of studying.
ETA: The Centauri used mass drivers against the Narn. That would do the trick.