The Anodyne Spirit, also known as the Dreadnought to the Covenant, was originally a Forerunner Keyship, designed to reseed the galaxy with life following the firing of the Halo Array. Following the reseeding of the San’shyuum on their homeworld of Janjur Qom, the ship was taken over by a fragment of Mendicant Bias, who attempted to use the ship to travel to Earth and make amends for taking the side of the Flood during the Forerunner-Flood War. There was a malfunction, however, and the ship crashed onto the surface of Janjur Qom, becoming partially buried after many centuries.
The partially buried Anodyne Spirit was eventually discovered by the San’shyuum and became a point of worship. Dissent eventually grew in the San’shyuum, between the Stoics who wanted to leave the Forerunner ship alone, and the Reformists who wanted to learn from and use Forerunner technology. Eventually the Reformers commandeered the Anodyne Spirit and left the planet in it, taking a large hunk of the planet with it. The Reformists used the knowledge learned on the ship to form the beginnings of the Covenant religion, including belief in the Great Journey.
Many years later the San’Shyuum met the Sangheili, which kicked off the War of Beginnings. Though the Sangheili were militarily superior, the San’shyuum were able to even the playing field due to their advanced technology, including the Anodyne Spirit. The war eventually ended in a truce, and the Keyship was converted into the power source for High Charity, the new home of the Covenant.
The Anodyne Spirit remained the power source of High Charity throughout the entirety of the Covenant, until its eventual destruction in 2552. After the Flood attacked High Charity at the end of the Battle of Installation 05, the ship was decoupled from High Charity and headed towards Earth, joining the effort to unearth the Portal at Voi. Once the portal was opened, the Anodyne Spirit traveled through it to the Ark, where is transported the Prophet of Truth to the surface. After a brief but intense Battle of Installation 00, the Ark and presumably the Anodyne Spirit, was destroyed by the firing of Installation 08.