From: Cortana, UNSC Pillar of Autumn shipboard AI

Re: SPARTAN-117 and the Destruction of Halo

Sir. As the rich data-bursts attached in this transmission make clear, we have been to hell and back. I'll be brief.

After Reach fell, I followed Cole protocol, and slipped the Pillar of Autumn. Using astronomical symbols SPARTAN 117 captured from a Covenant vessel, I chose an exit-vector that would place us in an uncharted system near a late- life gas giant planet (new classification, "Threshold"). To my considerable surprise, in orbit around the planet was an artificial ring construct, 10,000 kilometers in diameter.

Initially, I feared the ring was a Covenant installation. It was not. But the enemy has tracked us and was lying in wait around the ring. Rather than disk capture, Captain Keyes ordered my uploading into SPARTAN 117's neural network. While we abandoned ship, the Captain managed to land the Autumn on the ring, saving the lives of many of the crew.

- The Covenant referred to the ring as "Halo." It seems a prophecy about Halo's existence is central to our enemy's religion, and its discovery was cause for much celebratory chatter on the Covenant battle-network. During our initial operations on the surface of Halo, we encountered an alien artificial intelligence, designation "343 Guilty Spark." This AI claimed its primary purpose was tactical containment of a virulent, parasitic life form called "The Flood."

- Through a connection to Halo's deep data cores, I ascertained that the ring was built by an race of beings (referred to by the Covenant as "The Forerunners") as a weapon of last resort against the Flood. A sizable production of Flood was in stasis on the ring, and the Covenant, either by accident or design, released the parasite. Not their most brilliant maneuver.

- 343 Guilty Spark convinced SPARTAN 117 to activate Halo's primary weapon system and eliminate the Flood. The AI neglected to tell him however, that because the Flood consumes any suitable sentient host, Halo would make no distinction between the Flood and other life forms. In short: if Halo fired. it would destroy every thinking being in the galaxy. Human, Covenant, everything.

When we realized that Halo could destroy all life, SPARTAN-117 and I decided our only choice was to destroy Halo - stop 343 Guilty Spark from completing his assigned task, and deny the Covenant a weapon of unthinkable power. We used the Pillar of Autumn's fusion reactors to start a chain reaction that utterly destroyed the ring. I'm sorry to report that Captain Keyes was lost to the Flood.

With respect to out ongoing fight against the Covenant, our time on Halo was well spent. I have gathered a wealth of new information for our database of Covenant weapons, technology, tactics, and society. Additionally, SPARTAN- 117's proficient use of arms, and the destruction of the ring, resulted in a significant loss of enemy personnel and material.

That being said, I fear that the Covenant will not take kindly to our obliteration of their holy relic. Having thus struck the hornets' nest, we are now heading home with all speed.