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The Raider is the primary air/space superiority fighter used by the Cylons against the peoples of the Twelve Colonies of Kobol. There have been at least two designs used since the outbreak of hostilities between the two powers.
Cylon War-era Raider
During the Cylon War, raiders resembled a big "flying wing", and carried a crew of at least three Centurions piloting under the command of a specifically designated model. They are a mainstay in the Cylon arsenal of the time (TRS: "Miniseries", "Razor", Blood and Chrome).
Deployed en masse by the Cylon basestar, Raiders are used to great effect against Colonial battlestars and are nearly a match in maneuverability against their Colonial counterparts, the Viper Mark II and Mark III. They are also used as drop-ships for deploying ground forces (as seen in the Battle of Tauron) and are capable of vertical take-offs and landings, much like the Colonial Raptor (TRS: "Razor", Blood and Chrome).
Some forty years later, some Cylon War-era Raiders are still in active service. A contingent of Raiders is present aboard a lone Cylon War-era basestar which houses the First Hybrid. When the battlestar Pegasus inadvertently discovers this "Guardian basestar", a squadron of Raiders engages with the battlestar as well as its defending force of Viper Mark VIIs (TRS: "Razor"). A small number of original Raiders also appears at the Cylon Colony, shortly before its destruction by the Galactica (TRS: "Islanded in a Stream of Stars", "Daybreak, Part II").
The modern Raider, called sparrow in Colonial military jargon (TRS: "Maelstrom"), radically redesigned but still resembling its past incarnation as a giant flying wing, is first encountered 40 years after the Cylon War, when the Cylons launch their devastating surprise attack on the Twelve Colonies of Kobol. During this attack, Raiders transmit commands to Colonial vessels utilizing the Command Navigation Program (CNP). Compromised prior to the attack, the CNP was programmed with backdoors that permitted the Cylons to cut the power of any ship carrying the program (TRS: Miniseries).
This incarnation of the Raider is initially thought to be wholly mechanical in design, with a high-level AI controlling it. However, from inspection of a damaged Raider forced down in a firefight and recovered by Lieutenant Kara Thrace (TRS: "Act of Contrition"), the craft is found to be bio-mechanical in nature (TRS: "You Can't Go Home Again"), incorporating a number of large organs in its design, including a central brain. Raiders require an oxygen-nitrogen mix for their biological functions, and thus oxygen tanks are located somewhere onboard (TRS: "You Can't Go Home Again"). In effect, a modern Raider is a creature in itself.
Though Raiders are self-aware, their intelligence level is less than that of a humanoid Cylon and more like a trained animal (TRS: "Six Degrees of Separation"). Nonetheless, they are capable of independent thought and action, and can refuse to follow orders if they choose (TRS: "Six of One"). Much like the humanoids, the bio-mechanical Raider's consciousness resurrects in a new "body" if it is destroyed. While this allows the Raider to "learn" from its previous mistakes and become a more proficient killing machine, it can cause Raiders to develop what can be described as a desire for revenge after repeated deaths (TRS: "Scar"). Galactica's Viper pilots are regularly outnumbered and survive, indicating that Cylon Raiders are generally not matches for skilled human pilots.
The Raider is equipped with an FTL drive system (TRS: "Miniseries"). Following tests on the Raider captured by Galactica, this FTL system is found to be far more efficient in jump calculations than Colonial FTL systems. The drive shows its accuracy when Lt. Thrace takes the Raider from a point somewhere near the vicinity of Kobol back to Caprica in a single jump (TRS: "Kobol's Last Gleaming, Part I").
It is armed with conventional and nuclear missiles carried in internal wing bays and two pairs of kinetic energy weapons of different calibers mounted under the leading edge of the wings. Curiously, the only times the Raiders have been seen using their missiles are during the Fall of the Twelve Colonies and the Battle of The Colony. This may indicate that Raiders are not normally armed with missiles.
During the Battle of the Ionian Nebula, a Raider identifies one of the Final Five after their activation, causing all of them to refuse to fight further and forces the Cylons to retreat (He That Believeth In Me). Cavil (a Number One) concludes that the Raiders exceeded their programming, and to regain control over them the humanoid Cylons must reconfigure the Raiders' neural architecture and shave down their heuristic responses, essentially lobotomizing them and "dumbing them down." This decision leads to a violent split among the Cylons (TRS: "Six of One", "The Ties That Bind"). This split further leads to the Battle of the Resurrection Hub, resulting in the destruction of the resurrection technology used by both the Humanoid Cylons and the Raiders (TRS: "The Hub", "Sine Qua Non").
Heuristically-reconfigured Raiders participate in the Battle of The Colony against Galactica's Vipers. For the first time since the Miniseries, Raiders are outfitted with missiles and, using these weapons, destroy one of Galactica's gun batteries in the battle (TRS: "Daybreak, Part II").
With the destruction of The Colony and the Cylon forces lead by Cavil, as well as the loss of the resurrection technology, it is a foregone conclusion that the biological Raiders have gone extinct (TRS: "Daybreak, Part II").