This collection consists primarily of letters exchanged between Edison and Secretary of the Navy Josephus Daniels, along with related correspondence. Many of the typewritten letters are accompanied by drafts in Edison's hand. The three letters in this folder are from June-July 1917. They pertain to Edison's work on an instrument for locating a hostile airplane by determining the direction of the sound of its engine. There are also references to another device for finding the direction of submarines. The six photographs mentioned in the letters have not been found. However, a photograph of the airplane detector accompanies the description on pp. 186-187 of Lloyd N. Scott's Naval Consulting Board of the United States. One additional item pertaining to Report 39a July 5, 1917 letter from Edison to Danielscan be found in the Josephus Daniels PapersThomas A. Edison Correspondence, Library of Congress. Documents relating to Edison's work on direction finders can be also be found in Reports 6 and 13 and in Direction Finder (1917), Naval Consulting Board and Wartime Research Papers. Courtesy of Charles Hummel.