Anodyne Spirit

The Forerunner Dreadnaught was used by the Covenant to power all of High Charity. When the Flood attacked the city, the Prophet of Truth uncoupled the ship from High Charity's power grid and used it to travel to Earth. The Dreadnaught travels vertically, like a rocket. It is also capable of Slipspace travel.

A ship with enough power to power all of High Charity could likely move faster than any other ship in existence, which is quite impressive for a 100,000+ year old machine.

At the end of Halo 2, John-117 gets onboard the Dreadnaught, in his mission to kill the High Prophet of Truth. It is possible there is a Forerunner A.I. in the ship, the evidence being the presence Cortana found while trying to slow its launch sequence. . This ship is very geometric and angular in its design, and is estimated to be about 14 kilometers (8.694 Miles) tall.