Working and living in a confined space beneath the ocean (and sometimes the Arctic polar cap) demands a special kind of person. The Navy's submariners are all volunteers, carefully tested and screened and able to perform any job aboard, including steering the massive boat. During World War II, U.S. submarines sank more Japanese ships than did U.S. surface vessels and planes, but at a high cost: a twenty percent casualty rate. In the Cold War, nuclear submarines prowled the oceans, gathering intelligence or poised to launch a missile on command.