Effective July 1, William Swanson, a 31-year Raytheon veteran who was president of the Lexington, Mass. company, takes over as CEO. Swanson replaces Dan Burnham, who announced one day after presenting the company’s first-quarter financial results that he would leave the company. Burnham joined Raytheon in July 1998 from AlliedSignal, where he was president and COO. One of the 54-year-old Swanson’s most challenging tasks will be improving the performance of Raytheon’s money-losing Wichita-based aircraft unit.