Petty Officer, First Class
From Halopedia, the Halo wiki
Petty Officer, First Class, abbreviated to PO1, is a 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 Petty Officer Second Class, and subordinate to a Chief Petty Officer.
Work division supervisor.
- Halo: Official Spartan Field Manual - PART 8: UNSC ORGANISATION, NAVCOM Ranks, page 140-141