2549

May

 * May 21: Dr. Catherine Halsey flash clones herself in order to create the seed brain for the AI Cortana, infringing the UN Colonial Mortal Dictata Act in the process.

September

 * September 9: Fall of Arcadia. The Covenant glasses Arcadia.

November

 * November 7: Cortana is created from one of Dr. Catherine Halsey's flash-cloned brains.

December

 * December 15: A mandatory psychiatric reevaluation for the members of NOBLE Team takes place. Jun-A266 is noted as having "an unhealthy emotional detachment in regards to the consequences of his actions".

Unknown

 * Paris IV is attacked. According to ONI documentation, Staff Sergeant Avery Johnson uses a box of plasma grenades to buy time for his Marines to evacuate, receiving a twelve-hundred-rad cumulative dose of radiation and later being diagnosed with Boren's Syndrome, which in the future will save his life from Flood infection on Installation 04 and onward. However, the Borens' Syndrome story involving Johnson is a hoax, a fabrication by ONI to cover his participation in the much earlier ORION Project.
 * The 2549 edition of the Hog is released either this year or late in 2548.
 * The Covenant recall their standard Type-26 Wraith model to update its design, fitting a Type-52 DESW on a ring mount.
 * Sometime during this year, the SPARTAN-II program is announced to the public, and any Spartan who dies is to be listed as either Missing In Action or Wounded in Action, to give the illusion that Spartans never die in accordance with the Office of Naval Intelligence Directive 930.