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The modern basestars, seen some 40 years after the end of the Cylon War, are approximately the same size as a Colonial battlestar but appear to be more technologically advanced . The shape of the newer basestar reflects its name, with two Y-shaped hulls attached at their centers by a single pylon, the warship has a distinctive "star" shape.
They are equipped with a superior jump system and no visible means of sublight propulsion, lacking any engine pods or nacelles, but remain capable of chasing down a battlestar (TRS: "Exodus, Part II"). They can rotate their upper and lower halves into a tandem-Y configuration for entry into a planetary atmosphere (TRS: "The Plan").
Basestars operate a fleet of small fighters, known as Raiders, and are capable of deploying hundreds of these ships simultaneously (see Related Imagery). The enormous number of Raiders serves as a basestar's primary defense system.
Like the Raiders, the basestars are partially organic, which is particularly evident in their landing bays (TRS: "Kobol's Last Gleaming, Part II"). When severely damaged, they can sustain large, fleshy "wounds" (TRS: "Faith"). Moreover, Natalie mentions that their damaged baseship can heal itself (TRS: "Guess What's Coming to Dinner?").
The baseships possess several conventional rooms and hallways, which are sleek but generally bland. Lighting plays a large role in the aesthetics and some rooms are furnished with clearly human objects, such as beds and couches. Humanoid Cylons project different surroundings to navigate ship corridors more easily, and to provide them with an individually pleasing environment (such as a lush forest). Data and other functions (such as analyzing visual information) are handled within a liquid computer interface that resembles a stream of water flowing over a luminous glass surface. Cylons can interact with the main computer by placing their hands in these basins (TRS: "Torn").
Command and Control
A basestar is operated by many humanoid Cylons. Up to all seven models of them issue commands for the basestar from a central command and control center. Consensus amongst models is the typical procedure, as such the process of deliberation and voting on decisions may cause the basestar to react more slowly than a battlestar's command and control in a CIC.
A basestar's functions are managed by a partially humanoid Cylon incorporated into the ship, known as a Hybrid. The Hybrid, for all respects of identity and control, is the basestar. The ship is an extension of her body and she is the ship's mind. The Hybrid, despite its humanoid appearance, is not a considered a fellow humanoid Cylon and lacks voting power as other agents have in Cylon affairs.
A basestar has a datastream, or computer network, which interfaces with the Hybrid and all aspects of the basestar's operation.
A basestar is capable of launching conventional or nuclear missiles from 220 turret launchers mounted throughout the arms and central axis  that pivot to allow the basestar to fire in any direction. Basestar-launched nuclear strikes against Colonial ships are usually carried out before Raider deployment. One example of a Cylon nuclear attack involved three Cylon basestars that ambush the battlestar Pegasus. They open their attack firing several nuclear missiles before deploying Raiders and switching to a non-nuclear salvo (TRS: "The Captain's Hand").
A basestar's complement of Raiders is estimated as high as 792 fighters, not counting fighters in repair or otherwise off-line. It should be noted that there are a total of 864 Raider launch slots on the arms of a pre-retconned Basestar.  In comparison, the retconned Basestar has only 434 Raider launch slots, a dramatic decrease from the previous version.
This tactic, along with the massive numbers of Raiders that a basestar can unleash, suggest a reliance on overwhelming force to destroy a foe. It is probable that basestars used nuclear weapons to destroy the bulk of the Colonial Fleet (using their CNP back-doors to compromise their defenses first) in the opening wave of their destruction of the Colonies.
After the Colonial commanders draw away their Raider wings, two basestars are torn apart by the kinetic guns of the battlestars Pegasus and Galactica in a joint mission to destroy a Cylon Resurrection Ship. It would seem that that basestars rely heavily on their Raiders for close-range gun defense. Since a basestar does not appear to have point-defense batteries, or heavy armoring, it seems quite vulnerable to battlestars in close-range combat when fighter support is not prominent (TRS: "Resurrection Ship, Part II"). From this, it can be theorized that basestars are designed primarily as carriers for the massive fleet of Raiders they carry, rather than as a front-line main battleship. Their reliance on long-distance attacks with missiles and their complement of Raiders, as well as their overall fragility seem to support this.
This basestar belonged to the rebel Cylon faction comprised of only the Two, Six and Eight models aside from Boomer, as well as the last remaining Three copy later on. This basestar received serious damage after the other three models attempted to wipe out and destroy all of the rebel's basestars. All of the rebels' basestars – except for this – (TRS: "The Ties That Bind") were destroyed.
The basestar was later found by the Demetrius and its crew, who had been searching for Earth. They return to the fleet with the basestar, where the Colonials and the Rebel Cylons form an unsteady alliance to destroy the Resurrection Hub, and hence destroy the Cylons' ability to resurrect. However, the basestar becomes the only ship to make it there, after the Hybrid jumps without Galactica. Against all odds, the baseship manages to destroy the Hub with the help of the humans in the ship, as well as retrieve the last Three copy (TRS: "Guess What's Coming to Dinner?", "The Hub").
After a brief standoff, the Cylons join the fleet in the final jump to Earth, only to find it in ruins. The basestar is later invited to join the fleet to find a new home afterwards (TRS: "Sometimes a Great Notion").
Over time, the ship is integrated into the fleet, getting its own representation in the new Quorum of Ship's Captains and flying joint fighter CAPs with Galactica. Upon Admiral Adama's decision to abandon the battlestar, it is decided that the baseship would become the new flagship under Adama's command, since it is the only other warship remaining in the fleet.
When Galactica heads off to the Colony to rescue Hera, the baseship is left under the command of Admiral Hoshi to await Galactica's return. It later jumps to New Earth along with the rest of the fleet, where the Cylons turn control of the ship to the Centurions, allowing them to seek their own destiny as the human models settle on Earth with the rest of humanity.
Cylon War-era basestars
The Cylons had deployed three different variants of Basestars during the First Cylon War.
Much like its modern counterpart, this model utilized chemically-propelled missiles (with both nuclear and conventional warheads) as the main form of offensive weaponry. Raiders were deployed from access points (totaling 8 in number) throughout a basestar's hull to provide defense. This design, as with later iterations, was capable of operating within an atmosphere (Blood and Chrome).
The origins of the initial basestars are unclear. However, as Cylons were a creation of man in the early days before the war, it is probable that man himself (through the efforts of various colonies) designed the various ships and weapons used by the Cylons for the use in intra-colonial wars prior to the Articles of Colonization.
This configuration features two y-shaped hulls in tandem alignment, with a 1st variant-like top and bottom hull ("Blood and Chrome").
Although the main offensive armament of this variant is still its missile launchers, the ship also possesses numerous point defense cannons, which are used by one such ship in a failed attempt to deter the attacking Osiris's kamikaze run.
Third "Guardian" Variant
Towards the end of the first Cylon War, the Cylons built a prototype basestar that had roughly the same shape as the modern basestar. The first hybrids were developed for use with this model.
It is explained by Athena that a group of Centurions calling themselves Guardians fractured from the Cylon majority with such a basestar. The belief is that they escaped to the far reaches of space to avoid being shut-down in favor of their modernized, non-sentient successors (TRS: "Razor"). The only basestar of this type known to exist was destroyed by Colonial forces shortly after its discovery.