Toward a comprehensive nuclear test ban treaty : hearing before the Subcommittee on Arms Control, International Law and Organization of the Committee on Foreign Relations, United States Senate, Ninety-second Congress, second session, on S. Res. 230, to encourage a moratorium on underground nuclear weapons testing and to promote negotiations for a comprehensive test ban treaty and S. Res. 273, calling on the President to propose an extension of the nuclear test ban treaty to include underground testing, May 15, 1972.