Introduction to San Diego: San Diego is the only natural harbor in southern California. It controls the eastern waters of the Pacific Ocean and its geographical location is very important. This is the main support base of the U.S. 3rd Fleet. More than half of the fleet's ships, including aircraft carriers and nuclear submarines, use it as their home port. There are many warships parked in the naval port, and one of the huge ones is the most conspicuous, that is the famous retired USS Midway (CVB-41) aircraft carrier.