John F. Kennedy, the 35th U.S. president, lived with chronic back pain and undiagnosed Addison’s disease, which caused military doctors to initially reject him during World War II. Determined to serve, he eventually joined the U.S. Navy and took command of the patrol boat PT-109 in the Pacific. When a Japanese destroyer struck and split the boat, Kennedy’s quick decisions helped keep his crew alive. Even after hurting his back again, he swam for hours through the dark water while towing a badly