William Swanson, 54, has been elected chairman of Raytheon Co., effective January 28. He replaces Dan Burnham, 57, who will retire from the Waltham, Mass.-based parent company of Raytheon Aircraft. Swanson is a 31-year Raytheon veteran. On July 1 Swanson took over as CEO of Raytheon from Burnham, who joined the company in July 1998 from AlliedSignal, where he was president and COO.