Rebuilding the FleetHumanity, finally seeing a reprieve from decades of being on the defensive, used their unique position to recover the colonies they could and rebuild a fleet from the ashes. This fleet was led by a new flagship, the UNSC Infinity, which, while started eight years before the end of the war, was not battle-ready until months after, and not fully complete until 2557.
A New Class of SpartansIn parallel with rebuilding their fleet, the UNSC commissioned a new Spartan program to replace and build upon the Spartan programs of the past that had helped win the war. Deciding to use adult volunteers this time instead of abducting children, the Spartan-IV program created many more Spartan super-soldiers than the Spartan-II program ever did, and rivaled the output of the Spartan-III program. Though still significantly weakened by the loss of so many colonies and personnel, the UNSC was still able to use the newly created Spartans along with the UNSC Infinity to apply force when and where is was required.