Incorporating technology both reverse-engineered from Forerunner relics and captured from the Covenant, the UNSC Infinity is said to be the most technologically-advanced starship in the entire UNSC fleet. The ship is said to be almost six kilometres in length, having taken twenty years to finish construction, which only finished after the end of the Human-Covenant War . Launched in 2557 with a crew of 17,000 men and women, the ship is commanded by Captain Andrew Del Rio, and staffed with a full complement of both UNSC Marines, possibly including Orbital Drop Shock Troopers, and the new class of supersoldiers, the SPARTAN-IVs.
In the story of Halo 4, the Infinity picks up the distress signal emitted by the wreckage of the Frigate UNSC Forward Unto Dawn, and her two survivors, the Master Chief and the Smart AI Cortana. Responding to the call, the Infinity encounters the Forerunner shield world Requiem, which somehow disables all their electronic systems and then tows the ship inside itself with some kind of tractor beam. In order to survive a world crawling with both the zealots of the Covenant Remnant and a "race" of merciless Forerunner AI drones, the Master Chief and the crew of the Infinity will have to work together.