Naval Station Mayport (Admiral David L. McDonald Field)

Naval Station Mayport is a United States Navy base on San Pablo Island at Mayport, Jacksonville, Florida, on the St. Johns River near its mouth on the Atlantic coast. Owned by the Department of Defense and operated by the Navy, it falls under Navy Region Southeast and combines a deep-water harbor with an airfield, Admiral David L. McDonald Field.

The station is the headquarters of U.S. Naval Forces Southern Command and the United States Fourth Fleet, reactivated in 2008. Surface forces are administered by Commander Naval Surface Group Southeast, formed as Naval Surface Squadron Fourteen on 31 July 2015 from the merger of Destroyer Squadron 14 and the Cruiser-Destroyer Readiness Support Detachment Mayport, and renamed in 2024. The group's units are Arleigh Burke-class destroyers. Littoral Combat Ship Squadron Two, established at Mayport on 7 November 2014, administers the Freedom-variant littoral combat ships, nearly all of which are homeported at the station. Mayport is the third-largest surface fleet concentration in the United States. Aviation units comprise Helicopter Maritime Strike Wing, U.S. Atlantic Fleet, with squadrons HSM-40, HSM-48 and HSM-50; the field has been the East Coast base for LAMPS MK III helicopter squadrons since the Cold War. The Iwo Jima Amphibious Ready Group, assigned to Mayport between December 2013 and August 2014, has since departed, with Iwo Jima and New York shifting to Naval Station Norfolk in late 2021.

The protected harbor accommodates vessels up to aircraft carrier size and can berth some 34 ships. Repair work is handled by a ship's intermediate maintenance activity. The airfield has a single asphalt runway, 5/23, of 8,001 by 200 feet (2,439 by 61 m), able to take most aircraft in the Department of Defense inventory. The base area covers 1,680 acres (680 ha).

Built from 1939 and commissioned in December 1942 as a naval section base, the installation was reclassified as a Naval Sea Frontier base in 1943, with an adjoining naval auxiliary air station commissioned in April 1944; both closed after the Second World War. Mayport was reactivated in June 1948 as a naval outlying landing field, and in the mid-1950s the site was enlarged and the runway extended, with the new carrier basin first used by USS Tarawa in October 1952. The airfield was redesignated a naval air station in 1988 and merged back into the naval station in 1992 under post-Cold War consolidation. Conventionally powered carriers were homeported at Mayport until John F. Kennedy departed in 2007.