Correspondence, diaries, notebooks, reports, company files, clippings, printed matter, blueprints, plans, sketches, photographs, and other papers relating chiefly to Eastham's career as radio engineer and as head of the General Radio Company. Includes files pertaining to long-range navigation and the Loran project at Massachusetts Institute of Technology Radiation Laboratory. Also documents his avocation of collecting sixteenth- and seventeenth-century maps and atlases. Correspondents include Fred S. Barton, Cedric M. Benham, Ralph Bown, Vannevar Bush, Trevor Clark, K.T. Compton, James Bryant Conant, George Friedrichs, Nicole Friedrichs, Charles S. Grover, Alfred L. Loomis, Claude Lyons, Henry S. Mears, William P. Murphy, Marie E. Schaefer, and Henry Southworth Shaw.