The largest sectors of San Diego’s economy are defense/military, tourism, international trade, and research/manufacturing, respectively. The economy of San Diego is influenced by its deepwater port, which includes the only major submarine and shipbuilding yards on the West Coast. Several major national defense contractors were started and are headquartered in San Diego, including General Atomics, Cubic, and NASSCO. San Diego hosts the largest naval fleet in the world: it is home to 53 ships, over 120 tenant commands, and more than 35,000 sailors, soldiers, Department of Defense civilian employees and contractors. About 5 percent of all civilian jobs in the county are military-related, and 15,000 businesses in San Diego County rely on Department of Defense contracts.