NOTE: The following ship does not yet exist, and won't for centuries of In-RP time (which we probably won't even get to). Consider that fact before yelling that it's overpowered.Edit
The Leviathan is a truly massive ship. Not massive in the sense that a carrier is massive. Massive as in it took strip-mining three planets to the point where all there was left was floating chunks of rock (they even cooled down the metal cores of the planets, and used that metal too) to get enough raw matereals to build it.
Measuring an astounding seven kilometres in length, it is the single largest ship the engineers of Earth and it's colonies have, and most likely will ever construct.
The Leviathan is a massive 7km long, 750m wide, and twenty-three decks tall. It's main weapon is a massive MAC gun that has been dubbed 'Ragnarok', for obvious reasons. It's other armaments are a total of over 1,000 broadside guns, 500 point-defence systems, 30 PHASE drives, an unprecendentedly powerful Terawatt reactor, and twelve double-barreled ion cannons; plus massive amounts of missiles, lasers, etc.