ONI Section Zero is a subdivision of the Office of Naval Intelligence.
Starting in at least 2550, Section Zero began to monitor Subject D and Subject S, over their conversations about Atriox. This monitoring continued until 2558 when Subject D stopped communications with Subject S.
The most secretive section, Section Zero's existence is not general knowledge outside ONI. Details of its role and operations are limited. Based on the records of an AI named Melissa, it is thought to be ONI Internal Affairs, charged with rooting out and eliminating illegal programs. It is very discreet in its work. The true nature and activities of Section Zero are highly classified and unknown outside the ONI command hierarchy. Zero is, essentially, an internal investigations division that polices other ONI activities. Part of how Section Zero achieves this is through monitoring personnel communications.
This section has gained notoriety as the section that keeps and maintains sealed SPARTAN-I Program file archives, including Avery Johnson's. As Internal Affairs it enforces the rules and ensures standards are met. It is authorized to use lethal force in the course of its operations.