52 An idea of an illustrative range of postattack environments with levels of casualties, probable economic consequences, and the tentative identification of postattack situations under which the achievement of economic viability would be technologically feasible may be found in Winter, Sidney G. Jr., Economic Viability After Thermonuclear War: The Limits of Feasible Production, The RAND Corporation, RM-3436-PR (September 1963).Google Scholar For example, in an attack upon the United States in which out of 1000 to 4000 megatons, 750 to 2000 were delivered on nonmilitary targets, “the loss of industrial capacity would be a serious to insuperable obstacle [to economic] viability, unless extensive pre-attack preparations were made. Much would depend on whether the attacker [attempted] to maximize the economic difficulties created by the nonmilitary portion of the attack; … good to excellent fallout shelters would be required to keep casualties below 60 per cent of the population.” In order to deliver the megatonnage indicated on urban targets, from 375 to 1000 missiles with 2 MT warheads would have to impact, or a mixed force would have to deliver an equal amount of megatonnage in various-size packages, not counting the counterforce requirement. The Soviet missile force was estimated in late 1964 to be about 200 ICBM's, not all in hardened silos, and 142 submarine-launched ballistic missiles, a small percentage of which may be carried by nuclear submarines. An additional 250 bombers, 100 on two-way missions to the United States, 150 capable of reaching targets in Canada, Alaska, and the northwest United States, could be put by the Soviet Union over North America (McNamara, , Address before the Platform Committee; and Missiles and Rockets [January 4, 1965], 10Google Scholar). The United States had in 1965 850 land-based ICBM's, an additional 300 nuclear missiles in Polaris submarines, and 900 strategic bombers, half of them on a fifteen-minute alert (Johnson, President in his Defense Message to the 89th Congress, New York Times, January 19, 1965Google Scholar). By mid-1969, the United States is expected to have 1054 Minuteman and Titan intercontinental missiles, 656 Polaris submarine-launched ballistic missiles, and 678 intercontinental bombers (McNamara, in U.S. News and World Report, 53). An earlier version of Winter's study may be found in his testimony on civil defense before a subcommittee of the Committee on Government Operations, U.S. House of Representatives, 87th Cong., 1st Sess. (August 9, 1961), 303–30.