Galactica type battlestar
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The Galactica type battlestar is a Colonial capital ship that combines the functions of an aircraft carrier and a battleship . It was designed and deployed after the outbreak of hostilities between the Cylons and Colonials. A few ships of this class remain in service over 40 years after the end of the Cylon War; however, most were retired.
The class was designed and deployed by the Colonial Fleet in the early days of the First Cylon War, quite possibly as part of the Articles of Colonization, with 12 ships initially being built by, and representing, each of the Colonies (Miniseries). They included: Galactica, Columbia, Athena, and Archeron. They formed the lead ships of Cylon War era Battlestar Groups, and were represented in almost every major engagement of the War.
The original battlestars were space-going leviathans of more than 4700 feet (1400 meters) in length, designed to tackle the Cylon threat head on. They featured powerful gun batteries that ran up the center of the hull, numerous point defense turrets, and many missile silos, but their main show of force came from the multiple Viper stacks housed in the flight pods, which held up to a thousand Vipers. Initially, these stacks ran multiple stories, but were removed as the war died down (TRS: Blood and Chrome, Razor Flashbacks).
Unfortunately, the class didn't hold up well to the Cylon threat, with only the Galactica, Athena, and a third unnamed ship surviving the war.  Despite this, newer Galactica type ships were built, with newer technologies, which still remained in service at the time of the Fall of the Colonies. However, Galactica was never upgraded, and remained in its Cylon War outfit at the time of its retirement 40 years after the war. 
Eventually, the class is phased out in favor of the smaller Valkyrie type battlestars, and the newer Mercury class battlestars, however was inadvertently survived by the Galactica for nearly 5 years after the Fall of the Colonies.
The design common to Galactica and its sister ships can be broken down into two main sections: the main hull and the twin flight pods.
This comprises the bulk of a battlestar and can itself be divided into three sections:
The flight pods serve as the most critical feature of the battlestar. They are designed to launch and retrieve support ships such as Vipers and Raptors, as well as various other support craft such as Thera Sita, and even Colonial One. The pods on the Galactica type are designed to retract into the main body of the ship, primarily for FTL operations, and support ship transfers. Under normal operations, the pods are expanded out to provide a safe landing and support area for the ship's CAP. The pods also feature airlocks that can be used to dock the entire battlestar to a station or drydock for the safe transfer of personnel and equipment.
Each flight pod comprises two main decks for flight operations: the upper landing bay, which extends the full length of the pod, and the lower launch bays, which provide some 40 launch tubes per pod. The hangar deck, located under the landing bay, is used for maintenance, repair, refueling, rearming, and launch operations and runs the length of the flight pod.
Landing approaches are made from the stern. The preferred approach is a slow run into the landing bay, prior to making a vertical landing on a defined landing area (Act of Contrition). However, in emergencies, combat landings can be made, in which a craft approaches and lands at high speed on its landing skids (Miniseries).
Despite their massive size, battlestars are extremely maneuverable and can dock with space stations such as Ragnar Anchorage. Battlestars are not designed for atmospheric flight, although their hulls can manage a tenuous upper atmospheric storm like that surrounding the gas giant Ragnar (Miniseries) and can survive a jump and subsequent freefall into the atmosphere of a habitable planet (Exodus, Part II). A battlestar's FTL systems are capable of accurate jumps, able to place them in synchronous orbit above a relatively close planet and of placing them safely in the midst of an asteroid field (The Hand of God), a dense fleet of ships (Scattered), or a planetary atmosphere. However, they are grossly inferior to Cylon systems in terms of safe range (Kobol's Last Gleaming, Part I).
Battlestars are intended to operate for long periods without re-supplying. Their water purification capabilities alone are so efficient that, barring an emergency or unforeseen event, a battlestar can operate "for several years before replenishing" (Water). They also appear capable of undertaking large-scale repairs following battle damage (Miniseries, "Water"). They have ammunition assembly capabilities in the armory (Epiphanies) and may have small general fabrication facilities (Litmus). Vegetable stores and canned goods are kept in titanium lockers (Final Cut). Battlestars are capable of continuing combat operations despite suffering massive damage, as evidenced by Galactica's continuing effectiveness at defending the fleet years after the first Cylon attack and following several punishing engagements (He That Believeth In Me).
The original battlestar vessels deliberately avoided the use of networked primary computer systems during the Cylon War, as Cylon forces were adept at infiltrating and subverting such systems (Miniseries).
On Galactica, in the post-Cylon War era, these primary computers remained isolated by practice on order of its last pre-Holocaust commanding officer, William Adama. This no-networks practice saved Galactica from the fate of its sister battlestars in the Fall of the Twelve Colonies as Galactica's no-network order meant that the CNP, installed in almost all Colonial Fleet vessels at the time, could not be used aboard Galactica as the CNP was designed for use with a computer network.
In one dire instance in the early months of their exodus, Galactica networks its primary computers temporarily to aid in computation speeds for jump calculations needed to find the missing civilian Fleet (Scattered), but it is not without consequence. One or more computers are cracked during a Cylon attack with a Cylon virus, which proves resistant to removal and (weeks later) threatens the operation of the battlestar until the computers' hard drives are erased and restored from pre-Fall backup sets (Flight of the Phoenix).
During the First Cylon War, the Galactica type line of battlestars housed at least 5,000 crew and staff members on a fully operational ship, with many of these being support personnel such as Viper pilots, and Viper technicians. That number is drastically reduced following the Armistice, with many mustering out of service, and advancements in technology eliminating the need for certain service positions (for example, manned gun batteries). By the Fall of the Colonies, these and the newer Mercury class flagships, have a crew of no more than 2,500 to 3,000 people. In Galactica's case, it is suggested the ship is understaffed due to its decommissioning; however, the crew is still able to operate the battlestar, even in a time of war, with little to no loss of function .
Approximately twelve oxygen recirculation units are mounted throughout the ships of this class, which replenish oxygen as well as remove ("scrub") carbon dioxide from the air. These devices work continuously (Final Cut).
Ships of the Line