Commander

In the United States Navy, the United States Coast Guard, the United States Public Health Service Commissioned Corps, and the National Oceanic and Atmospheric Administration Commissioned Corps, commander (CDR) is a senior officer, with the pay grade of O-5. Commander ranks above Lieutenant Commander and below Captain. Commander is equivalent to a lieutenant colonel in the other uniformed services.

A Commander in the U.S. Navy may command a frigate, destroyer, submarine, aviation squadron or small shore activity, or may serve on a staff (typically as first officer). An officer in the rank of commander who commands a vessel may also be referred to as "Captain" as a courtesy title, or informally referred to as "skipper."

Historically, the rank of "Commander" was originally called "Master Commandant" in the U.S. Navy. This rank corresponded in function to "Master and Commander" in the Royal Navy. It was later changed in 1838 to its modern form.