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Titans at 15km long supercapitals, they come with a giant 'doomsday' superweapon which will incinerate a regular capital ship in one shot, they carry smaller Capital sized weapon batteries and have the ability to support regular fleets with their jump bridge capabilities and jump clone facilities.
Building one of these in game takes months, and costs the equivalent of 3-4000 US dollars if you were to convert PLEX rather than making the money in game (depending on the exchange rate).