The Crew Capsule Dockable is small stage similar to a Crew Capsule, but is dockable.
During rocket assembly, it is pre-loaded with 1 Battery, 1 Oxygen Tank and 1 Carbon Dioxide Scrubber. These three Cargo items may be removed/replaced during assembly, or in space after launch. Additionally, it's equipped with a parachute which can be deployed during the latter stage of capsule Atmospheric entry into a planet's atmosphere.
It is Atmospheric entry capable and its thrusters are capable of propelling it backwards, just like the basic module.
It is based off of the Apollo capsule, which was used from 1966 to 1975 throughout the Apollo and Apollo applications programs.