From Halopedia, the Halo Wiki
Petty Officer First Class is the sixth enlisted rank of the UNSC Navy and is a non-commissioned officer. It is equal in rank to Staff Sergeant in the UNSC Marine Corps.
In informal settings, Petty Officers First Class are typically called "Petty Officer".
- ↑ This is the insignia for a U.S. Naval Petty Officer First Class in the Hospitalman rating. However, in Halo 3 the insignia for Master Chief Petty Officer is shown to be the same as for the U.S. It is inferred that this applies to all UNSC Navy Enlisted rank insignes.