One of an undisclosed total number of Battlestars constructed by the Twelve Colonies of Man. Eight other Battlestars are specifically named in the series: (Acropolis, Atlantia, Columbia, Pacifica, Pegasus, Rycon, Solaria, and Triton). Galactica represents the Colonial planet Caprica, and is crewed mostly by Capricans. Galactica was built 500 yahren before the close of the Thousand Yahren War (and the start of the television series). It is believed to be the only Battlestar to survive the Destruction of the Twelve Colonies, until Battlestar Pegasus is found.
Of the other ships, it is known that the Atlantia, Acropolis, Pacifica and Triton are destroyed at the Battle of Cimtar in "Saga of a Star World". Battlestar Columbia is stated in the episode "Gun on Ice Planet Zero", but it is said to also have been destroyed at Cimtar by a Centurion. The Rycon is mentioned in passing in the episode "Take the Celestra" as the ship of Captain Kronus. Pegasus is encountered in "The Living Legend".
Galactica is commanded by Commander Adama. It has a complement of about 150 Vipers: a mixture of its own, some from the other battlestars at the Peace Conference, and a large number of fighters from the Pegasus.
Novelizations based on the original series, various comic books, and other sources have named several other Battlestars, including Bellephon, Cerberus, Olympia, and Prometheus.
Galactica entered service in the early years of the Cylon War, under the command of Commander Nash. During her service, Galactica formed a part of Battlestar Group 75 (BSG 75), a Colonial force described by series creator Ronald D. Moore as a mixed-force of vessels somewhat similar to a US Navy carrier battle group.
Like any of her sister ships, which may have survived the original Cylon War, Galactica underwent refits and upgrades (for example, at the end of her career she was equipped with the latest Mark VII Viper space superiority fighter). However, her computer systems were neither networked nor integrated by any of her commanding officers, up to and including her current commander, William Adama.
Due to this lack of network integration at the time of the Cylon attack, Galactica was immune to the infiltration program used by the Cylons to disable Colonial vessels and defense systems, using the Command Navigation Program (CNP), developed by Dr. Gaius Baltar and subverted by Cylon operative Number Six as a back door into such systems.
At the time of the Cylon Attack, Galactica was 50 years old and she was undergoing formal decommissioning from the Colonial Fleet following her retirement as an operational vessel. She had been due to become a museum ship; a combined living museum commemorating the Cylon War and educational center. Due to its age, the ship is unofficially known as "The Bucket" by the crews of both Pegasus and Galactica. Another nickname used by the crew is "The Big G" (a possible reference to the U.S. Navy sailors' nickname for USS Enterprise, "The Big E").
Since the Cylon attack, in keeping with the concept of the original 1978 series, Galactica has become both protector and provider to a small fleet of civilian vessels searching for the legendary planet Earth.
Galactica took heavy damage during its raid on New Caprica, and her hull is now clearly darker with burn marks and missile hits. The starboard hangar deck, which had been converted into a museum prior to Galacticas intended decommissioning, was used to house civilian refugees from New Caprica after the evacuation, and earned the nickname "Camp Oilslick". In "A Measure of Salvation", which followed "Torn", Major Lee Adama informs Galactica that their Raptor is now on approach to the starboard landing deck, which indicates that the starboard flight pod is starting flight operations again.
In the episode "The Passage" Galactica was once again used to house fleet passengers during the trip through the intense gas cloud, leaving the fleet vessels to be flown by skeleton crews with radiation medication. It is unclear as to whether the passengers have been returned to their vessels between "The Passage" and "The Eye of Jupiter".
In the episode "The Woman King", 300 additional passengers are shown being moved to the starboard hangar deck, and the area was given the name "Dogville" by the Galactica crew. Upon arriving, each passenger was checked for medical issues by civilian doctors and medical staff. Also now housed in the starboard hangar deck is a makeshift bar called "Joe's". It is located behind a storage area, and has a bumper-pool table, Pyramid arcade area, and a heavily damaged Mark II Viper hanging above the bar. It was first seen in the episode "Taking a Break from All Your Worries".
Galactica has been seen taking hits from nuclear weapons. Though the ship suffered damage, she is still operational. It is unclear exactly how well rated the Cylon nuclear weapons are versus Galacticas armor. Also, as the nukes detonated outside of the vessel, most of the energy would have been directed and attenuated out into the area of least resistance: space.
At the onset of the series, Galacticas last operational squadron of Mark VII vipers participated in the decommissioning ceremony before departing the ship. The squadron was re-directed to intercept a group of cylon fighters and was subsequently disabled by the cylon computer virus and destroyed. The museum display Vipers, mostly Mark II's, were pressed into service to defend the ship, and these, along with a small number of Mark VII's (presumably refugees from other battlestars or spares broken out from storage) comprised the ship's fighter compliment until the arrival of the Pegasus midway through the second season. Pegasus possessed construction facilities and flight simulators that allowed it to build and train new Mark VII vipers to strengthen the squadrons of both ships. When Pegasus was destroyed during the liberation of New Caprica, her nearly intact squadrons were transferred to Galactica, giving the latter a full compliment of Vipers. By the time of the episode He That Believeth in Me, there were more Vipers available than qualified pilots, and trainees (known as 'nuggets') were pressed into service to defend the fleet.