Petty Officer, Third Class
From Halopedia, the Halo wiki
Petty Officer, Third Class, abbreviated to PO3, is an enlisted rank in the United Nations Space Command Naval Command (NAVCOM) rank structure; including the UNSC Navy and Office of Naval Intelligence. It is preceded by Crewman, and subordinate to a Petty Officer Second Class.
Work party lead.
- Halo: Official Spartan Field Manual - PART 8: UNSC ORGANISATION, NAVCOM Ranks, page 140-141