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Construction and First War Service (YR48-YR60)
Galactica was one of the first twelve Galactica type battlestars to be constructed by the Colonials, each representing one of the twelve colonies; Galactica represented Caprica. While solidly built, various factors during Galactica's construction led to the shipyard "cutting corners" when it was originally built, with various components not completed to spec (TRS: "No Exit").
These battlestars were all designed with non-integrated computer systems to avoid the Cylons' demonstrated ability to override or subvert networked command and control systems early in the war (TRS: Miniseries, Night 1). Rather than technological sophistication, the battlestar depended on its sheer bulk and defensive / offensive capabilities to ward off any threats to itself or the Colonies.
Entering service sometime prior to the tenth year of the War, Galactica's primary duties included planetary defense, and border patrol. It is unknown if the ship took part in any major engagement prior to this point, however it is known that the Colonials were facing heavy losses in the wake of Cylon advancements (Blood and Chrome).
Two years later Galactica participated in Operation Raptor Talon, along with Columbia and one other battlestar of its class. It was successful in inflicting major damage to Cylon forces, but not before they were able to destroy Columbia. The battle ended in a draw, when it was announced the Cylons had signed an armistice agreement (TRS: "Razor").
Modern Service and Decommissioning (YR80-YR00)
Post War Service
Even before the end of the War, Galactica undergoes a refit that sees the removal of much of its armor, removal of the Viper stacks, and many of its dorsal primary batteries. Major changes to the layout of the CIC, hangar decks and infirmary are delivered at this point as well (TRS: "Razor Flashbacks").  This would be Galactica 's last major refit prior to its decommissioning nearly 40 years later. Galactica never receives the networked computer or Baltar's CNP upgrades like its sister ships do.
Following the armistice, the Galactica is regulated to intra-system duties, and has been known to take on "Coast Guard" roles involving the shipping sector, which limits the use of the ship's two FTL drives. Prior to Galactica's FTL jump to Ragnar Anchorage, its drives were not utilized in nearly twenty years (TRS: Miniseries, Night 2).
With its active career drawing to a close, a decision was taken to retire Galactica and decommission it from service. The Colonial Fleet chose not to scrap the ship, but to turn it into a combination of living museum to the original Cylon War and an educational center, with the conversion being overseen by the vessel's final commander, William Adama.
At the time of its formal decommissioning ceremony, Galactica is stripped of all but one of its operational Viper Mark VII squadrons, its munitions are destroyed, and its starboard landing pod is converted into a pressurized museum which houses various items from the Cylon War. However, its Viper munitions stores are still on the ship. The museum is about to open when the Cylons break the Armistice, and renew their hostilities with the Colonials.
Cylon Attack and Post-Fall Exodus (YR00-YR04)
With the renewed and unexpected Cylon hostilities, Galactica is quickly brought back to combat condition and sorties a squadron of Mark IIs retrieved from its museum, engaging in its first battle with the Cylons in over forty years (all but one last Mark VII squadron were sent to Caprica for reassignment). It survives a direct hit by a tactical nuclear missile to the forward section of its port flight pod, and later jumps successfully to Ragnar Anchorage to replenish its empty ammunition stores at this strategic depot.
Galactica emerges from the anchorage and engages one basestar with its gun batteries, providing cover for a fleet of 75 civilian ships harboring survivors of the Twelve Colonies. Once the entire civilian fleet successfully jumps away, and as a second basestar approaches to join the battle, Galactica recovers its remaining Vipers and jumps to the rendezvous point beyond the Red Line, never to return to Colonial space (TRS: Miniseries, Night 2).
Leading a Ragtag Fleet
Since the exodus of the Colonials from their overrun homeworlds, Galactica becomes both protector and provider for the Fleet. It provides covering fire for the Fleet during Cylon attacks no fewer than 240 times (TRS: "33": "Act of Contrition"). The battlestar provides much of the Fleet with recycled water (TRS: "Water") and it is the primary source of medical care, where groups of civilians are periodically brought aboard for check-ups and treatment (TRS: "Litmus"). Galactica also undertakes internal policing duties within the Fleet (TRS: "Water", "Bastille Day").
Galactica successfully goes on the offensive against the Cylons, after the capture of a tylium fuel mining and processing plant in the process. This plant is able to provide enough fuel for Galactica and the fleet for years (TRS: "The Hand of God").
The advanced battlestar Pegasus, commanded by Rear Admiral Helena Cain, joins Galactica approximately 6 months into their exodus (TRS: "Pegasus"). While integration into the fleet is far from smooth, the two battlestars work in unison to destroy two Cylon basestars, as well as a critical Cylon support ship known as a Resurrection Ship (TRS: "Resurrection Ship, Part II").
Following the founding of New Caprica, Galactica is assigned to the orbital defense force that protects the planet. During this time the majority of the crew are allowed to the surface in an effort to populate the planet and restore the human race, a majority of whom are seemingly convinced that the Cylons will never find New Caprica. The diminished crew inevitably results in standard maintenance becoming overlooked or ignored; basic military responses, such as the launching of alert fighters and routine training exercises become difficult to execute. One year following the founding of New Caprica, a fleet of Cylon ships jump into orbit of the planet. Severely limited in their abilities, Admiral Adama orders the defense fleet to jump away from New Caprica along with a handful of civilian ships still in orbit of the colony. (TRS: "Lay Down Your Burdens, Part II").
Four months after their escape, Galactica's staff is still in the process of developing a rescue strategy with 16 training exercises having been completed, and a 17th underway when an accident causes its early cessation (TRS: "Occupation"). This forces both a change in strategy and the reformulation of a rescue plan to deal with personnel who have not seen conflict in 16 months (TRS: "Precipice", "Exodus, Part I").
After coordinating with the New Caprica Resistance, Galactica leaves Pegasus to guard the space-bound members of humanity, while it initiates the Battle of New Caprica. In the subsequent battle, Galactica is outnumbered by four basestars, lacks the support of its Vipers, and missile barrages disable its FTL drives. Pummeled by the Cylons, Galactica faces destruction when Pegasus unexpectedly arrives. Pegasus's salvos draw the attention of the basestars away from Galactica, buying the crew time to bring its FTL drives back on-line, recover its planes, and escape (TRS: "Exodus, Part II"). Galactica bears the scars of the battle with significant scorching and dents to the hull. Repairs continue on the journey through the Ionian nebula, with heavy damage to secondary storage, and damage to one particular airlock nearly causing the deaths of Galen and Cally Tyrol during what they expected to be a quick repair of a hull micro-fracture (TRS: "Blood on the Scales", "A Day in the Life").
Given the loss of Pegasus, Galactica now boasts a larger crew, Viper and Raptor complement, to the point where there are more pilots than there are ships to fly (TRS: "Torn"), although the training of new recruits is still ongoing (TRS: "Dirty Hands", "Crossroads, Part II", "He That Believeth in Me"). Further, there are various redundancies between the two crews that are appropriately dealt with (TRS: deleted scene from "Exodus, Part II").
Resuming the Search for Earth
Galactica takes aboard a significant quantity of civilians following the exodus from New Caprica, as several civilian ships are lost during the escape from the failed colony. Cramped conditions increase as crew and civilians struggle to adapt to life back aboard a ship. The civilians reside on the refurbished starboard hangar deck as a refugee camp nicknamed "Camp Oil Slick" and later "Dogsville" (TRS: "Torn", "The Woman King").
During a food shortage crisis caused by contamination of the Fleet's food processing systems, Galactica (along with its Raptors acting as pilot ships) guides the civilian Fleet through an area of intense heat, light and radiation caused by a dense star cluster to reach edible resources on the algae planet. Galactica's heavy armor and radiation shielding protect it from the intense effects of the cluster, but the ship still suffers hull damage and numerous decompressions.
When the Fleet reaches the Ionian Nebula, four Cylon baseships are detected following an unexplained power outage. With the entire Fleet powered down and unable to escape, Galactica scrambles its Vipers and prepares for a lopsided fight, outnumbered and outgunned (TRS: "Crossroads, Part II"). During the following battle, Galactica manages to hold off the main attack of the massive Cylon attack force. Despite the damage suffered in previous engagements, the old warship wields its main guns and point defense batteries effectively again in defense of the Fleet. Despite having the advantage, and managing to destroy or damage several civilian ships, the Cylons retreat in the middle of the battle, after detecting one of the Final Five among the Colonials. Galactica takes minor damage in the battle, losing a forward dorsal battery, and contributing to further weakening of its overall structure (TRS: "He That Believeth in Me").
After three years of searching, Galactica and its Fleet locate Earth. The fleet enters orbit, and immediately launch ground teams who quickly determine that the planet is uninhabitable, having suffered a cataclysm sometime prior. A short time after, Galactica leads its fleet back to the stars (TRS: "Revelations", "Sometimes a Great Notion").
With Galactica's advanced age, the corners cut during construction, and the abuse it has been put through since the war started all have contributed to deteriorating conditions. A structural survey of the ship finds several torn supports and weakened areas in the hull, and a more in-depth examination finds endemic metal fatigue throughout the ship, with virtually every part of the hull riddled with small cracks and fissures. A plan is proposed to treat the damaged parts of the ship with an organic Cylon resin from the Rebel Baseship, which would fill the cracks and bear the stresses, which Adama at first refuses. However, Adama finally appreciates Galactica's dire condition when he finds a tear in a bulkhead in his quarters, and orders Tyrol to carry out his plan to repair the ship (TRS: "No Exit"). Despite the resin, Galactica is dying of old age and accumulated battle damage.
Despite repairs, the ship continues to accrue damage, and the order is given to abandon ship. Command will be transferred to the Cylon baseship once supplies and personnel have been offloaded (TRS: "Islanded In a Stream of Stars"). The ship is to be stripped of all useful equipment, including its Viper launching mechanisms. However, inspired by a photo of Hera on the Memorial Hallway, Admiral Adama decides to commit the old battlestar to one last mission: a suicidal mission to rescue Hera from the Cylon homeworld, the Colony. With Starbuck's help, he puts a line of red tape down the center of the hangar deck and makes an impassioned speech to the gathered crew members: He will lead Galactica to rescue Hera, but it is a volunteer mission only. If there are not enough people to crew Galactica, he will instead lead a Raptor assault with anyone willing to join him. Everybody makes their choice; there are enough people to crew the ship. Preparations for the final mission get underway. Command of the Fleet is transferred to Louis Hoshi, the flag is transferred to the baseship and a number of Vipers are assigned to it for CAP duties.
Battle of The Colony
With a skeleton crew and a frail battlestar, Admiral Adama executes a daring mission to rescue Hera Agathon.
Galactica jumps to the Colony at point-blank range. Besieged by the Colony's gun batteries at first, the ship is pummeled relentlessly (causing the destruction of its dorsal Colonial roundel and heavy structural damage all around the ship) until Samuel Anders, recently injured and turned into a Hybrid, manages to take them and the Colony's Hybrids offline. As Galactica's Vipers engage incoming Raiders, its Raptors jump directly from their berth in the starboard flight pod, causing the destruction of the pod, and maneuver to board the Colony. Galactica is then used to ram the Colony, providing an entry and exit point for assault teams but crumpling its forward alligator head.
As the battle wages on, Cylon Raiders swarm Galactica, destroying at least one of its remaining heavy gun batteries. Cylon forces manage to blow a hole in Deck 21, allowing them to pour into the ship at platoon strength. Legions of enemy Centurions swarm into the ship, and are held back by marine firing squads, despite inflicting heavy casualties. After a brief cease fire, the ship comes under enemy fire once more, in one final push by Cylon forces. After the Colony is hit with nuclear-tipped missiles launched by Racetrack's drifting Raptor, both Galactica and the Colony begin falling into the black hole the Colony was orbiting.
Battered by interstellar debris, Galactica is successful in escaping its position via a blind FTL jump (though Starbuck inputs coordinates she extrapolated from the Music). The ship however does not retract its flight pods before executing the jump. This and the accumulated stresses of the past four years turn out to be the nail in the coffin for the old battlestar. Successfully emerging from the jump, Galactica suffers a series of catastrophic failures across its entire structure. Its lateral structural supports give out, which causes sections of the hull to visibly flex and twist against each other, so much so that hull breaches and explosive decompression rock the ship, sending structural beams ripping through decks, causing electrical failures and destroying multiple systems in the CIC. As the hull flexes, several Vipers are in turn tossed from the port flight deck. Despite the damage, the ship remains in one piece thanks to the Cylon organic resin, and other vital ship systems like life support and sublight propulsion are online. Galacticas FTL is offline, and the ship cannot jump without risking destruction. It is, for all intents and purposes, beyond repair. The fear of being stranded in space is short lived as the ship is revealed to have exited its jump above the moon of a habitable planet within sublight range.
When the Colonials decide to colonize this world, Galactica and its fleet are scuttled, piloted directly into the system's star, by Samuel Anders. Admiral Adama is the last soul to leave the ship, departing in his Cylon War-era Viper Mark II (TRS: "Daybreak, Part II").
Before the attack, Galactica has approximately 2,900 crewmen. By the time of the arrival of Pegasus, attrition has reduced this number to about 2,660. (c.f. Crew tally) It is unknown whether the Colonial Marines account for members or not.