Colonizers

Ultramassive colony vessels sent to populate worlds. Colonizer typically carry 100,000 or more people in addition to massive amounts of equipment and support material. Furthermore, they are modular and highly automated; in a Home Standard Environment they are capable of building sustenance level quarters with redundant power sources in two weeks and a completely functioning city with extended services (including public transportation) for up to a quarter million people within one year.
There were 14 Colonizers built, and half of these are serving more as Relocation Assistance Vessels (essentially large scale ferries). They are HUGE and challenging to maintain. Moreover, being able to move 100,000 people and the necessary resources to create a colony has tremendous impact on world/system development, thus, only the Major Houses have the clout to successfully request one's use and only a couple actually own one.
The average preparation and deployment cycle is 5 years: the trips between star systems themselves typically only take weeks! Upon arriving, the ship (a task force in itself, actually) verifies landing areas, launches the preparation modules and First Landers and it's 3 months before the main body of colonists actually settle the planet. Within the next 3 months the entire ship and its cargo can be deployed to the planet.
As with most Federacy starships, the ship is modular, and the vast majority of the ship is left behind on the planet, eventually becoming the material and infrastructure for the primary and secondary planetary or system settlements.