The second and third digits denotes the officer's area of specialization within the Line, Staff Corps, LDO or Warrant Officer communities.
The final (fourth) digit denotes the officer's current type of commission.
An officer of the Regular Navy whose permanent grade is Ensign or above
An officer of the Regular Navy whose permanent status is Warrant Officer or Chief Warrant Officer (NOTE: Warrant Officer (pay grade W-1) is not currently used in the U.S. Navy; all U.S. Navy Warrant Officers are currently commissioned as Chief Warrant Officer 2 (pay grade W-2))
A temporary officer of the Regular Navy whose permanent status is enlisted
An officer of the Regular Navy who is on the retired list
No longer used
An officer of the Naval Reserve (NOTE: Exceptions are designators with a 4th digit of 7, 8 or 9)
An officer of the Naval Reserve on active duty in the Full Time Support (FTS) Program, previously known as the Training and Administration of the Reserve (TAR) Program; includes officers of the FTS Program rotated to other than FTS billets
An officer of the Naval Reserve who was appointed in the Naval Reserve Integration Program from enlisted status or whose permanent status is Chief Warrant Officer, Warrant Officer or enlisted
An officer of the Naval Reserve who is on the retired list
Between Fiscal Year 1992 until Fiscal Year 2005, all officers entering the U.S. Navy were awarded a Reserve commission (commissioned as Ensign, USNR). Legislation was signed that all Reserve Officers on full-time Active Duty, previously designated by a "5" in the last digit of the designator, would be converted over to a Regular Navy commission by the close of Fiscal Year 2006.
Today, there is no distinction between USN and USNR Officers, no matter what the commissioning source. All hold the same ranks, have the same responsibilities and authority, and enjoy the same privileges. As part of the U.S. Navy's Active Reserve Integration (ARI) initiative that "operationalized" the Navy's Reserve Component, the term "U.S. Naval Reserve" was superseded by "U.S. Navy Reserve" and the term USNR was discontinued as a matter of Total Force policy in 2005. All officers in the U.S. Navy now use the term USN with their rank titles.
§Fully Warfare Qualified Unrestricted Line (URL) Officers
Unrestricted Line Officers (URL Officers) are commissioned Officers of the Line in the United States Navy who are qualified to Command at Sea the Navy's warfighting combatant units such as warships, submarines, aviation squadrons and SEAL Teams. They are also qualified to command the higher echelons of those units such as destroyer and submarine squadrons, aviation wings and groups, and special warfare groups. At the Flag Officer level, they also command carrier strike groups, expeditionary strike groups, task forces, and Fleet and Force commands. URL officers are also eligible to command shore installations, facilities and activities directly supporting the Navy's warfare mission.