Naval Station Mayport (IATA: NRB, ICAO: KNRB, FAA LID: NRB) is a major United States Navy base in Jacksonville, Florida. It contains a protected harbor that can accommodate aircraft carrier-size vessels, ship's intermediate maintenance activity (SIMA) and a military airfield (Admiral David L. McDonald Field) with one asphalt paved runway (5/23) measuring 8,001 × 200 ft. (2,439 × 61 m).

Since its commissioning in December 1942, NS Mayport has grown to become the third-largest naval surface fleet concentration area in the United States. Mayport's operational composition is unique, with a busy harbor capable of accommodating 34 ships and an 8,001-foot (2,439 m) runway capable of handling most aircraft in the Department of Defense inventory.

Naval Station Mayport is also home to the Navy's United States Fourth Fleet, reactivated in 2008 after being deactivated in 1950.

The base has historically served as the homeport to various conventionally powered aircraft carriers of the Atlantic Fleet, including Shangri-La (1960 - 1971), Franklin D. Roosevelt (1956 - 1977), Forrestal (1977 – 1993), Saratoga (1957 - 1994), and, most recently, John F. Kennedy (1995 - 2007). With the decommissioning of all conventionally powered aircraft carriers by the U.S. Navy, no carriers are presently assigned to Mayport. However, both houses of Congress have passed legislation authorizing about US$75 million for dredging and upgrades at NAVSTA Mayport to accommodate a nuclear-powered aircraft carrier.

On January 29, 2010, the Quadrennial Defense Review Report stated that a nuclear aircraft carrier would be homeported at NAVSTA Mayport. The action will help protect the fleet against a potential terror attack, accident or natural disaster, because all east coast aircraft carriers are currently based at Naval Station Norfolk, Virginia, according to the report. West coast aircraft carriers are split between Naval Air Station North Island in San Diego, California, Naval Base Kitsap and Naval Station Everett in Washington state and one carrier assigned to the Forward Deployed Naval Force (FDNF) homeported at Naval Base Yokosuka, Japan.

In 2009 Robert Gates, Secretary of Defense, stated, "Having a single (nuclear carrier) homeport has not been considered acceptable on the west coast and should not be considered acceptable on the east coast." The decision was opposed by elected officials in Virginia, who would lose 3,500 sailors and their dependents, $425 million in revenue each year, and most importantly, 6,000 support jobs. The Hampton Roads Chamber of Commerce estimated the loss at 11,000 jobs and $650 million per year. Infrastructure changes and facility construction at Mayport are estimated to take five years and cost over half a billion dollars. The 2011 budget commits $590 million during the fiscal years from 2011 to 2019, so a carrier may not move to Mayport until 2019. However, an amphibious group is coming sooner. USS New York (LPD-21) relocated to Mayport in December 2013 and USS Iwo Jima (LHD-7) and USS Fort McHenry (LSD-43) also switched their homeports to the naval station in August 2014.

The Virginia congressional delegation has fought the loss of even one of NAVSTA Norfolk's aircraft carriers boost to their economy by citing other areas such as shipbuilding to spend the Navy's tight budget.

A 2013 report from the Navy revealed that they are considering basing as many as 14 littoral combat ships at NS Mayport. Littoral Combat Ship Squadron 2 was established at the base on November 7, 2014. USS Milwaukee (LCS-5), USS Detroit (LCS-7), USS Little Rock (LCS-9), and USS Sioux City (LCS-11) will be among the squadron's ships.