It indeed is apart of a US Naval Base. It is designated Naval Amphibious Base (NAB) Coronado. This portion of the island was created (and yes I mean created) in 1943 when the harbor was dredged to allow for larger ships. The base was commissioned in 1944. It is used to train navy SEALS and is the only amphibious base on the West Coast. Other than that, I have no further information.