The King Arthur is a Babylon-Class Cruiser made by the CMF in response to the the destruction of the CMF Galahad at the hands of the Archangel Super-Cruiser. Its designs were originally made to combat the UNSC-Infinity Class Super-Cruiser, but were later scrapped due to the creation of the Galahad; however, when the Galahad met its match against the Archangel, the Babylon designs were revived, revised, and upgraded, and the King Arthur was commisioned immediately. After barely defeating the Archangel, the KA was hauled into an orbital repair station, and was later transported via the Galahad to an undisclosed CMF shipyard for reconstruction and refit.
The King Arthur is the onyl ship of its class, and is designed to be a "Titan Killer", eliminating large targets like super-cruisers. It accomplishes this goal with the combination of a lot of heavy armor, and an abundance of hard-hitting weaponry like its iconic Heat-Blade. The ship is designed in a modular way, such that allows the relatively simple transformation from "Conquest Mode" (used for travel) to "Vanquish Mode" (Used in combat against other ships), and visa versa.
The "Retribution Blade" that the King Arthur uses goes along with it's theme of "Avenging the Fallen CMF Fleet" which were the result of the Archangel Super Cruiser (which it was designed to kill specifically). This is due to the fact that it is made of the melted down and refined hulls of the fallen Omaha Class Super-Space-Battleships, lost in the Battle of Earth. The King Arthur also deploys all 24 of these ships's oversized Mass Driver Cannons, allowing the ship to pack a heavy punch to any Foe.
When going against Super-Cruisers or large amounts of normal ships, the King Arthur will transform to its "Vanquish" Mode, increasing it's combat efficiency many times over. This allows it to use its gigantic Heat Blade as a sword, use the modified MAC in its right arm (modified to reload quickly), and to open all gun ports to reveal the devestating array of 24 oversized Mass Drivers, utilizing High-Explosive rounds. The maneuverability of the ship is also increased many times over in this form, allowing the KA to maneuver (to scale) with that of a trained soldier. This quick movement makes the KA a very deadly foe, and was the main reason it was able to survive long enough in the fight against the Archangel. IT should be noted that in this form the KA can also land planetside and "walk"; however, this was only used as a last resort to stop the transformed remains of the Archangel, and was not included in the designs.