Naval Station Mayport 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 with one asphalt paved runway (5/23) measuring 8,001 × 200 ft. (2,439 × 61 m). The station was commissioned in December 1942. It was reclassified as a Naval Sea Frontier base in 1943. A new naval auxiliary air station (NAAS) was established in April 1944.