Over the next four years, the U.S. Navy is transferring six Los Angeles class attack submarines (SSNs) from the Atlantic to the Pacific. Three of the boats will be based in San Diego, one in Bangor, Washington and one in Pearl Harbor, Hawaii. This will result in 31 SSNs based in the Pacific, and 21 in the Atlantic. Normally, two SSNs accompany each deployed carrier task force. Otherwise, the SSNs are sent out individually on patrols, or specific missions. SSNs have been used increasingly for intelligence collecting work. The shift of SSNs to the Pacific is in recognition of the greater potential need in the Pacific. That means the growing Chinese fleet, and ongoing problems with North Korea and Iran.