Petty officer, third class

Petty officer third class is the fourth enlisted rank in the U.S. Navy, U.S. Coast Guard, and the United States Naval Sea Cadet Corps, above seaman and below petty officer second class, and is the lowest rank of non-commissioned officer, equivalent to a corporal in the U.S. Army and Marine Corps. Petty officer third class shares the same pay grade as senior airman in the Air Force, which no longer has an NCO rank corresponding with E-4.

Unlike seaman and lower ranks, a sailor's advancement to petty officer third class is not automatic given time in service, but is also contingent on performance evaluations by their superiors and rate examinations (tests of specialty knowledge), except for certain technical ratings which carry automatic advancement to PO3 after successful completion of that rating's "A" school and fulfillment of time in rate requirements. The advancement cycle is currently every 6 months. Only a certain number of billets (job openings for a given rank) open up biannually and all seamen compete for promotion. The top scorers are chosen for advancement, but only in sufficient numbers to fill the billets available.

Petty officers serve a dual role as both technical experts and as leaders. Unlike the sailors who rank below them, there is no such thing as an undesignated petty officer. Every petty officer has both a rank and rating (job, similar to an MOS or AFSC in other branches). The rank and rating combined are known collectively as a sailor's rate. A petty officer's full title is a combination of the two. Thus, a petty officer third class who has the rating of Aviation Structural Mechanic is called an Aviation Structural Mechanic Third Class. The term petty officer is only used in abstract, the general sense, when referring to a group of petty officers of different ratings, or when the petty officer's rating is unknown.

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