The United States stockpiles 93 commodities having strategic and critical importance to national defense. To determine stockpile policy and goals for these commodities, the Federal Preparedness Agency (FPA) of the General Services Administration (GSA) uses a mathematical model to estimate what the requirements of the Nation's wartime economy will be. The FPA modifies the model based on inputs from the Departments of Commerce, Defense, State, and the Interior. Inputs are estimates based on data showing what past experience has been and expert judgment as to what a future situation could be in time of war. In 1976 the FPA determined that the Nation's silver stockpile of 139.5 million troy ounces exceeds national defense requirements. GSA has requested congressional approval for the phased sale of this inventory.