" To achieve a global ban on nuclear testing, my administration will immediately and aggressively pursue U.S. ratification of the Comprehensive Test Ban Treaty . After more than five decades of talks, it is time for the testing of nuclear weapons to finally be banned . " President Barack Obama, April 2009. "I will begin working to build the necessary bipartisan support for US ratification of the Comprehensive Nuclear Test Ban Treaty ... success would be the single greatest arms control accomplishment for the new Senate and it would reestablish America's traditional leadership role on nonproliferation." Senator John Kerry, Chairman, Senate Foreign Relations Committee, January 2009. ***** The Comprehensive Nuclear-Test-Ban Treaty (CTBT) would ban all nuclear explosions. It was opened for signature in 1996; as of June 2009, 180 nations have signed it, and 148 have ratified. Entry into force requires ratification by 44 nations with nuclear reactors specified in the treaty, of which 35 have ratified as of June 2009. The remaining nine are China, Egypt, India, Indonesia, Iran, Israel, North Korea, Pakistan, and the United States. The U.S. Senate rejected the treaty, 48 for, 51 against, 1 present, in 1999, far less than the two-thirds majority needed for Senate advice and consent to ratification. As the opening quotations indicate, the Senate seems likely to take up the CTBT again in the next few years, possibly before the Nuclear Nonproliferation Treaty review conference that begins in April 2010. If the Senate reconsiders the treaty, Senators would need to arrive at a net assessment of whether the treaty is in U.S. security interests. There are at least two complementary paths to a net assessment. One involves debating pro and con arguments to weigh the treaty's potential benefits, costs, and risks. The main arguments for the treaty are that it would prevent other nations from developing nuclear weapons of advanced design (or of more advanced design, in the case of Russia and China), would improve U.S. standing to press other nations to support nuclear nonproliferation efforts, and would improve the ability to detect clandestine nuclear tests. The main arguments against are that nations could conduct undetected clandestine tests that could affect the military balance, strong U.S. nuclear forces restrain nuclear proliferation by convincing allies and friends that they do not need nuclear weapons of their own, and nuclear testing is the only way to be sure that U.S. nuclear weapons will work as intended. (CRS Report RL34394, Comprehensive Nuclear-Test-Ban Treaty: Issues and Arguments , presents these arguments in detail.) A debate, however, may change few minds, as each side typically presents its arguments and rebuts those of the other side. A second path involves efforts to alter the net assessment through measures intended to mitigate perceived risks of the treaty. This path has been taken in earlier nuclear testing treaties through "Safeguards," unilateral measures consistent with the treaties that the United States can take to buttress its nuclear intelligence and weapons. Safeguards were first proposed by the Joint Chiefs of Staff in 1963 in connection with a nuclear testing treaty, and have been updated several times since. To address concerns about the reliability of U.S. nuclear weapons, Safeguards mandate steps for this nation to take to maintain these weapons, with testing if necessary. To address concerns about other nations' intentions, Safeguards mandate an improvement in U.S capabilities to monitor nuclear programs of other nations. More specific goals of current Safeguards include: Maintain modern nuclear laboratory programs, attract and retain experts in nuclear technology, and improve U.S. nuclear weapons in areas significant to the U.S. nuclear posture; Maintain the ability to return to nuclear testing if needed to retain confidence in the safety, security, and reliability of these weapons; Maintain and improve the ability to monitor nuclear weapon programs of other nations and related efforts that could support these programs; and Maintain and improve the ability to detect clandestine tests of nuclear weapons that could be militarily significant. Safeguards may be a central element in any debate over the CTBT. Senators supporting the treaty may seek to draft a package of Safeguards that could win the votes of enough skeptics to cross the 67-vote threshold for advice and consent to ratification. Opponents may assert that there is no substitute for testing so that Safeguards are moot, or insist on a package so robust that supporters would find the benefits of the CTBT not worth the costs. For example, some supporters could see Safeguards under which the United States sustains its nuclear weapon enterprise for the foreseeable future as undermining efforts to enhance U.S. nonproliferation credentials. Safeguards may be of particular interest to Senators who have not decided how to vote on the treaty. Some Senators in this group may see pros and cons as in balance and look for something that tips that balance. Some may seek a way to strengthen the case for their vote politically. Some may see the treaty as offering advantages only if other steps could compensate for its perceived risks. Some may feel that the United States would lose little by ratifying the CTBT on grounds that this nation is highly unlikely to conduct future nuclear tests, while seeing in the CTBT debate an opportunity to gain a commitment to steps to augment U.S. security as the price for their votes. Even if this group is small, it can be critical: a few Senators can affect legislation decisively, as congressional consideration of the American Recovery and Reinvestment Act shows. Yet an analysis of CTBT pros and cons would not address these concerns. Arriving at a package of Safeguards and any measures to implement them would entail bargaining, which is a different legislative process than debating in that debate often does not change votes whereas bargaining often does. At issue for the Senate is whether or not a resulting bargain could change the Senate's net assessment of the treaty enough for that body to give its advice and consent to ratification. This report presents the Safeguards, updates them, discusses their implementation, and considers implications for CTBT ratification. Limits on nuclear testing have been proposed since the dawn of the atomic age. In 1946, Representative Louis Ludlow introduced H.Con.Res. 146, declaring the sense of Congress that, among other things, an atomic bomb test be canceled. Limitations have been on the international agenda since 1954, when Prime Minister Jawaharlal Nehru of India proposed "Some sort of what may be called 'standstill agreement' in respect, at least, of these actual [nuclear] explosions." The United States, United Kingdom, and Soviet Union held extensive talks on the subject beginning in the mid-1950s without reaching an agreement. The Cuban Missile Crisis of 1962 led President Kennedy to accelerate the push for a test ban to ease U.S.-Soviet tensions and address public concerns over radioactive fallout. Talks held in Moscow in July 1963 initially focused on a CTBT, but negotiations foundered, as they had many times in the preceding years, on monitoring of underground tests. Instead, negotiators agreed to the Limited Test Ban Treaty (LTBT), which banned tests in the atmosphere, in space, and under water, where confidence in monitoring capability was much higher. During the 1963 debate on ratification of the LTBT, the Joint Chiefs of Staff expressed concern that the treaty would lead to "euphoria" and cause the United States to let down its guard against the Soviet Union. They conditioned their support for the treaty on four Safeguards: (a) The conduct of comprehensive, aggressive, and continuing underground nuclear test programs designed to add to our knowledge and improve our weapons in all areas of significance to our military posture for the future. (b) The maintenance of modern nuclear laboratory facilities and programs in theoretical and exploratory nuclear technology which will attract, retain, and insure the continued application of our human scientific resources to these programs on which continued progress in nuclear technology depends. (c) The maintenance of the facilities and resources necessary to institute promptly nuclear tests in the atmosphere should they be deemed essential to our national security or should the treaty or any of its terms be abrogated by the Soviet Union. (d) The improvement of our capability, within feasible and practical limits, to monitor the terms of the treaty, to detect violations, and to maintain our knowledge of Sino-Soviet nuclear activity, capabilities, and achievements. Senators wanted assurance that these conditions would be met. To this end, Senate Majority Leader Mike Mansfield and Senate Minority Leader Everett Dirksen met with President Kennedy. In a letter of September 10, 1963, President Kennedy offered them "unqualified and unequivocal assurances" on the treaty. These assurances included the Safeguards set forth by the Joint Chiefs (though differently worded), and provisions regarding Cuba, East Germany, and nuclear explosions for peaceful purposes. These assurances were instrumental in securing Senator Dirksen's support, and with it, that of the Senate. The Senate gave its advice and consent to ratification on September 24, 1963, by a vote of 80 to 19; the LTBT entered into force October 10, 1963. ( Appendix A includes several sets of Safeguards.) A key uncertainty in 1963 concerned the value of underground nuclear testing, as reflected in Safeguards A and C. Such testing, however, soon proved to be of great value. In 1971, Carl Walske, Assistant to the Secretary of Defense for Atomic Energy, stated that the nuclear test program since 1963 has made the difference between having fairly reliable knowledge about vulnerability, both during the launch and the reentry phases [of ballistic missiles], and not having it; between having the Poseidon and Minuteman III systems, and having systems which at best could be a fraction as effective in terms of effects on defended targets; and between the possibility of an effective ABM, and most likely, no such possibility.