The hangar deck is where a battlestar's fighters and support ships, such as Vipers and Raptors, are stored and maintained between missions. The hangar deck is located under the landing bay of each flight pod.
When a Viper or Raptor returns from a mission, they are moved to the many landing platforms above the hangar deck, which is a special airlock that lowers the spacecraft from the landing bay to the hangar deck in a continuous motion.
Basic repairs, fueling and munition loading take place on the hangar deck. During Condition One alerts, pilots scramble to their fighters. For Viper flight, the deck crew pushes Vipers out into the launch tubes, which are accessible through doors of the hangar deck. Raptors are returned to the landing bay with the landing platforms for their launches; launch tubes are designed for use by Viper-class fighters only.
If a launch is aborted, the deck crew is called upon to pull the fighter out of the tube for quick repair. The hangar deck is basically as well-manned as the deck of any real-world aircraft carrier.
Deck Chief Galen Tyrol is responsible the overall repair and readiness of all combat spacecraft on battlestar Galactica.
Currently, only Galactica's port hangar deck is available for missions. The starboard hangar deck is empty as the port flight pod was to become a museum on the battlestar's scheduled decomissioning (Miniseries). Launching spacecraft here is problematic since many of the facilities here were stripped for the expected museum. The expanse of the empty starboard hangar deck has been used as a temporary morgue as well as an assembly hall for speeches to the crew at large.
Other special space fighters, such as captured Cylon Raiders, Heavy Raiders, and the experimental Blackbird are stored away in the hangar deck as well.