I came across a few field items at a storage estate sale. one of which I can't seem to find ANY information on. Was wondering if anyone can tell me anything about it or knows where I might find info, or if it has any real value. It is a field phone. overall good condition, the plaque on the front reads "A.B. Portable Tel. System, manf. by Dictograph Products. Inc. for Bureau of Yards and Docks U.S.N". Does anyone have any information?