These vessels are expensive in materials & research, and are very late game. These act like drop pods, but are not one use - when you bring it back home you choose where to land and disembark. They can load people and cargo and bring it somewhere else - potentially a very long distance, and back again.
These are tiered, flying ships with very specific roles. The SRTS Expanded Mod adds new types of transportation ships to send pawns and resources all over the world.