Petty Officer

Petty Officer is a term used for a range of non-commissioned officer ranks in the UNSC Navy, such as;
 * Petty Officer Third Class
 * Petty Officer Second Class
 * Petty Officer First Class
 * Chief Petty Officer
 * Senior Chief Petty Officer
 * Master Chief Petty Officer

While the first three ranks are generally referred to as "Petty Officers," ranks from Chief Petty Officer and up are more correctly termed "Chiefs."