The most powerful warship ever built, the UNSC Infinity has seen significant action since its initial deployment in 2553 at the Siege of Kolaar. It stands at over three miles long, making it not just the largest warship, but the most expensive single project humanity has ever attempted. Construction on the Infinity began in 2544, long before the end of the war, but well after the UNSC was aware at how overpowered the Covenant was against them. The ship was initially designed to double as an ark ship, carrying the remainder of humanity to safety after the Covenant had destroyed all human colonies. Though it never served that purpose, it does support a crew of over 18,000 people, making it a city unto itself.
The Office of Naval Intelligence initially funded the project in its entirety, but costs quickly ballooned enough that the UNSC had to be included in the budgeting. Because the project was to be built in secret, the Infinity was built in a secret shipyard located within the Oort cloud around the Sol system. Even with the Infinity being such a large line-item for the UNSC and ONI, and perhaps because of it, it was not operational for nine years after construction started, and did not officially enter service for thirteen years.
THE FLAGSHIP OF THE UNSC
Although the Infinity has only seen service for a few years, and none of which were during the Human-Covenant War, the ship has still seen significant combat, including both theaters on Requiem, and several battles leading up to Operation: ATHENA, where the UNSC battled Jul 'Mdama's Covenant for control over the Forerunner Absolute Record. The Infinity has also been the target of at least two terrorist attacks, including from the United Rebel Front in 2553, and the New Colonial Alliance in 2558.