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.