The Crew Module Dockable is similar to a Crew Module, but is dockable. During rocket assembly, 1 Battery, 1 Oxygen Tank and 1 Carbon Dioxide Scrubber are pre-loaded in it. These three Cargo items may be removed/replaced during assembly, or in space after launch.
It is equipped with a parachute which can be deployed during the latter stage of capsule Re-entry into a planet's atmosphere.
In real life, it is used to carry astronauts into space, and transport them to stations or other spacecrafts.