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 one item in this folder is a letter from Edison to Daniels, dated June 16, 1919. It pertains to a depth cartridge designed to enable a navigator to ascertain the depth of water under his vessel. The cartridge could also be used as a safety signal in fog. The photograph enclosed with the letter has not been found; a sketch that probably relates to the invention appears on the back of Edison's handwritten draft. This idea was previously mentioned in Report 14.