UNSC Military Security Code 447-R27 is a UNSC protocol enforced in 2552. It forbids a consultant from accessing classified files in ONI's CASTLE Base on planet Reach. AIs guard the database against this. In event of an infraction, the offense is recorded and authorities are immediately notified. The AI then warns the infractee to stop, and is authorized to use whatever force necessary if the infractee will not comply. Dr. Catherine Halsey and her AI broke this protocol during the Battle of Reach, which led her to Ackerson's SPARTAN-III Program on Onyx.