The capsule was a small auxiliary craft which launched from the underside of Federation Starfleet Constitution-class starships. The capsule was a circular design, featuring a large transparent bubble like canopy.
In 2266 the USS Enterprise's capsule was launched during crew disembarkation after the Enterprise had landed on the home planet of a race of Robots. Later Captain Kirk and Spock, along with a Robot guard, used the capsule to reboard the Enterprise to access one of the ship's power rods. (TOS comic: "UK comic strips, first story arc")