Dr. J. R. Dunning circulated this internal "restricted" letter just months prior to the bombing of Hiroshima. It was distributed to an engineering department (called S.A.M. Laboratories and located at Columbia University) that was working on the Manhattan Project. The letter thanks members for their outstanding work and dedication to the project. This copy belonged to Mildred Goldberg, a secretary, who unknowingly typed out scientific formulas for this top secret wartime operation and later collected the documents contained in this exhibition.