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 documents in this folder are from March 1917. They pertain to Edison's experiments on a phonographic range finder (also known as an audible range finder) that would detect the position of enemy guns by their sound. Photographs relating to the invention are included with Edison's report. Additional material about the range finder can be found in Report 6 and in Direction Finder (1917), Naval Consulting Board and Wartime Research Papers. Correspondence regarding a related invention, the Aeroplane Detector, can be found in Report 39.