The physics involved with these improved designs is beyond the scope of this book; some details are given in Atomic Bomb [1]. But a sense of the enormous legacy of the Manhattan project can be gleaned by examining some statistics regarding the growth of nuclear arsenals worldwide since 1945. In the discussion which follows, bear in mind that many countries do not readily divulge information on their nuclear forces; these numbers are best estimates by knowledgeable observers of nuclear affairs. The graphs and tables herein are adopted from Atomic Bomb with some updates as appropriate.
No country that perceived itself as a world power could be without its own nuclear deterrent. The Soviet Union (now Russia) detonated its first atomic bomb, essentially a copy of Fat Man based on information transmitted from agents at Los Alamos, on August 29, 1949. Subsequently, the United Kingdom, France and China developed their own nuclear weapons (1952, 1960, 1964). The United States, Russia, the United Kingdom, France, and China are now known as the ‘primary five’, or ‘P5’ nuclear weapons states; table 7.1 summarizes some P5 nuclear milestones. The British first tested a full-scale fusion weapon in 1957; the Chinese followed in 1967, and the French in 1968.
Table 7.1. Some nuclear milestones for the P5 nuclear states. (Source [2, 3].) See also table 7.2.
Table 7.2. Estimated worldwide nuclear warheads, 2013–2016. All numbers should be rergarded as approximate. Data from [5, 8–14]. Note: In [9] the authors estimated a United States stockpile of 4670 warheads. This estimate was prepared before the Defense Department release cited in the text; the authors attribute their overestimate to more warheads having been retired than they had predicted based on preceding average retirement rates.
In addition to the P5 countries, four other nations are also recognized as nuclear powers: India tested its first weapon in 1974, Pakistan in 1998, and North Korea in 2006. Israel is widely regarded as having acquired nuclear weapons in the 1960s and to possess a stockpile on the order of 80 devices, but maintains a policy of official ambiguity by never having formally declared itself as a nuclear power. Other countries such as Iraq, South Africa, Iran, and Libya had nuclear weapons programs but have abandoned them.
An excellent source of information on nuclear weapons deployments is the bimonthly magazine Bulletin of the Atomic Scientists, which features a regular series of articles under the title Nuclear Notebook prepared by Hans Kristensen and Robert S Norris. In a 2009 article [4], these authors estimated that the United States produced over 66 500 nuclear warheads of 100 different basic types and variants of types between 1945 and 2009. The bomb type of which the most were built was the W68 warhead (yield 40–50 kilotons); over 5200 were deployed on submarines between 1970 and 1991. Some tactical warheads were small enough to be carried by a single person. In the current United States arsenal, the highest-yield warhead is the 455 kiloton W88, which is mounted on submarine-launched ballistic missiles (SLBMs). On the Russian side, the highest-yield weapons are carried by Inter-Continental Ballistic Missiles (ICBMs), and are rated at 800 kt. Figure 7.1 shows the post-war growth of deployed numbers of weapons, that is, those readily available for use. The number peaked in 1986 at about 69 000, but has since been considerably reduced due to the effects of various arms-control treaties between the United States and Russia.
Figure 7.1. Estimated global nuclear weapons inventories, from [5]. Included in the Total curve are ‘smaller’ nuclear powers (United Kingdom, France, China, Israel, India, Pakistan), which in 2013 were estimated to hold a total of about 1100 weapons. Data for the US and Russia do not include a total of ∼5000 ‘retired’ warheads awaiting dismantlement (table 7.2).
Such a spectrum of designs and possible missions naturally demanded an extensive testing program. Between 1945 and 1992, the United States conducted 1030 nuclear tests, plus an additional 24 in conjunction with the United Kingdom. Some tests involved multiple warheads; the total number of detonations involved was 1149. As illustrated in figures 7.2 and 7.3, the United States conducted the most tests.
Figure 7.2. Distribution of 2056 nuclear tests worldwide by year. The totals for 1958 and 1962 are 116 and 178 tests. For 1958, (US, USSR, UK) = (77, 34, 5); for 1962, (US, USSR, France, UK) = (96, 79, 1, 2). The scale is set to a maximum of 80 to make visible the small numbers of tests in some years. The Soviet Union has not tested since 1990, nor the United States since 1992. The Hiroshima and Nagasaki bombs are not included here as they are considered to be combat weapons, not tests. Individual country scores as of 2017: (US, USSR, France, UK, China, India, Pakistan, North Korea) = (1030, 715, 210, 45, 45, 4, 2, 5). Data from Natural Resources Defense Council; see also [6].
Figure 7.3. Distribution of 2045 P5 nuclear tests 1945–1996. (US, USSR, France, UK, China) = (1030, 715, 210, 45, 45). The UK figure includes 24 tests conducted underground in the United States. Not included here are one Indian test in 1974, three Indian tests in 1998 comprising five claimed detonantions, two Pakistani tests in 1998, and five North Korean tests in 2006, 2009, 2013, 2016 (2 tests).
Tables 7.2 and 7.3 list current estimated warhead deployments and types of delivery systems. In table 7.2, ‘Deployed’ warheads are defined as those on missiles or at bases with operational launchers, whereas the ‘stockpiled’ column includes both deployed and reserve units. ‘Total Inventory’ figures are the sum of stockpiled plus retired weapons. Figures made public by the Department of Defense in early 2016 indicated that the United States’ stockpile of deployed weapons as of the end of fiscal year 2015 (September 30, 2015) was 4571; see [7].
Table 7.3. Current distribution of warheads by delivery platform. Data from [5, 8–14].
This number is rounded to 4570 in table 7.2; the release did not address how many warheads are retired and awaiting dismantlement. The United States figure of 2070 deployed weapons includes some 180 non-strategic bombs deployed in Europe. The stockpile figure for Russia includes ∼1850 non-strategic weapons. Of the 160 deployed United Kingdom weapons, 48 are normally deployed on submarines at sea, and of the 290 deployed French weapons, about 80 are normally deployed on one or two submarines at sea.
The decrease in the number of nuclear tests beginning in the early 1960s and the dramatic drop in the number of deployed warheads beginning in the latter half of the 1980s is attributable to the effects of various test-ban and arms-reduction treaties. Some of these are described in the following section.
7.2 Nuclear arms treaties and the baggage of the Cold War
In the 1950s, public concern with atmospheric nuclear tests began to mount with the measureable presence of radioactive fallout that was entering the food chain. In August, 1957, President Dwight Eisenhower announced that the United States would suspend nuclear testing for up to two years if the Soviet Union agreed to a cessation of production of fissionable materials for weapons and the installation of an inspection system to ensure compliance. No agreement was (or has yet been) reached on limiting fissile materials production, but the Soviets responded that they would unilaterally halt all nuclear tests, provided Western nations (the United States and Britain) also stopped testing. In the meantime, technical experts convened in Geneva through the spring and summer of 1958 to consider issues involved in a test ban, concluding that a ban could be verified through a worldwide network of monitoring stations. On October 31 of that year, the then nuclear powers of the world, the United States, Britain, and the Soviet Union, began negotiations on a comprehensive nuclear test ban. All three countries also began a one-year testing moratorium, which explains the gap in figure 7.2 at this time.
In August, 1959, as negotiations continued, President Eisenhower extended the United States moratorium to the end of that year; the Soviets announced that they would not resume testing so long as the Western powers continued to observe a moratorium. The American self-moratorium expired on December 31, at which time Eisenhower announced that America felt free to resume testing, but would not do so without advance notice. A few weeks later, however, the French carried out their first test. International tension
s began rising with the construction of the Berlin wall in August, 1961, and the Soviets resumed atmospheric testing on September 1 of that year. The Soviets carried out 59 tests over the remainder of that year; the United States responded with a series of underground tests beginning on September 15, and resumed atmospheric testing in the spring of 1962.
Despite these setbacks, progress was made on a proposal to ban atmospheric testing. The result of these negotiations was the Limited Test Ban Treaty (LTBT). This treaty prohibits nuclear weapons tests or any other nuclear explosions in the atmosphere, in outer space, under water, and in any other environment if such explosion causes radioactive debris to be present outside the territorial limits of the country under whose jurisdiction or control such an explosion is conducted; it does not prohibit underground tests. The LTBT came into force on October 10, 1963. At present, it has been ratified by 126 nations (‘states’, in UN legal parlance), with 10 others having signed but not yet ratified. A number of smaller counties have not signed the LTBT, but two notable large non-signatories are France and China.
Perhaps the most significant nuclear agreement is the 1970 Treaty on the Non-Proliferation of Nuclear Weapons, which is known as the NPT. The NPT recognizes two classes of countries: Nuclear Weapons States (NWS), which in 1970 comprised the P5 countries, and Non-Nuclear Weapons States (NNWS). A total of 190 nations are party to the NPT, but four nuclear powers are not: India, Israel, Pakistan and North Korea. (North Korea acceded to the NPT, but later withdrew; the treaty gives signatories the right to withdraw upon 3 months notice.) Under the terms of this treaty, the P5 states agree to not transfer ‘nuclear weapons or other nuclear explosive devices’ and ‘not in any way to assist, encourage, or induce NNWS to acquire nuclear weapons’. For their parts, NNWS states agree not to ‘receive, manufacture or acquire’ nuclear weapons or to ‘seek or receive any assistance in the manufacture of nuclear weapons’. They must also accept safeguards mandated by the International Atomic Energy Agency to verify that they are not diverting nuclear research from peaceful uses to nuclear weapons programs. The treaty allows for transfer of nuclear technology and materials to signatory countries for the development of civilian nuclear energy programs, so long as they can demonstrate that those programs are not being used for the development of nuclear weapons. While the treaty also imposes a vague, non-binding, obligation on all signatories to move in the general direction of nuclear and total disarmament, the NPT imposed no restrictions on the number of warheads that NWS could possess. The United States and Russia have negotiated separate warheads-numbers pacts (below), but at present there is concern in the arms-control community that a lack of ongoing negotiations could threaten the future viability of the NPT.
The most ambitious effort to halt nuclear testing altogether is the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which would ban all nuclear explosions in all environments for any purposes. It was adopted by the United Nations in September, 1996, but it has not yet entered into legal force as five signatories (China, Egypt, Iran, Israel, and the United States) have not yet ratified it; India, Pakistan, and North Korea have not signed the treaty. The US Senate rejected ratification of the CTBT in October, 1999, over concerns that other countries could easily cheat. However, the argument that violations could go undetected is no longer sustainable. The Preparatory Commission for the Comprehensive Test Ban Treaty Organization, which is headquartered in Vienna, was created to build a verification system comprising a worldwide network of detection and analysis facilities which include seismological, hydroacoustical, infrasound, and radionuclide sensors. The sensitivity of the system is evidenced by the fact that fission products from the low-yield underground North Korean test of 2006 were readily detected at a monitoring station in northern Canada. A cheater might conceivably get away with a very low-yield nuclear explosion, but such a weapon would be of little practical value.
Even though the United States has not ratified the CTBT, it has abided by its provisions, and has not conducted a nuclear test since 1992. This, however, raises an important issue: if weapons cannot be tested, how confident can one remain of their safety and reliability as they age? In response to this, the National Nuclear Security Administration has established the Science-Based Stockpile Stewardship program. In this program, weapons components are routinely subject to analyses to monitor their aging processes, and they can be refurbished or replaced as needed. At least one new weapon in the current US arsenal, the Earth-penetrating B61 Mod-11 bomb, was deployed without testing in 1996.
Other treaties limit numbers of warheads. The first such effort was the 1991 Strategic Arms Reduction Treaty (START) between the US and the USSR, which limited these countries to deploying no more than 6000 warheads atop a total of 1600 ICBMs, SLBMs, and bombers. By late 2001, this had resulted in the removal of about 80% of all strategic nuclear weapons then in existence. START was succeeded by the Strategic Offensive Reductions Treaty (SORT) of November 2001, which called for both sides to reduce operationally deployed strategic warheads to 1700–2200 by 2012. The most recent agreement is the ‘New START’ treaty, which was signed by the US and Russia in April, 2010. This treaty requires these two countries to reduce their arsenals to 700 deployed ICBMs, SLBMs, and heavy bombers, with a total of 1550 warheads on deployed ICBMs, SLBMs, and ‘warheads counted’ for heavy bombers. The total number of deployed and non-deployed ICBM launchers, deployed and non-deployed SLBM launchers, and deployed and non-deployed bombers is separately limited to 800. Table 7.4 shows some estimated eventual warhead numbers. The New START numbers for the US are based on assuming 420 Minuteman III missiles, with each carrying a single warhead; 240 SLBMs, each of which carries four warheads; and 60 bombers. According to the treaty’s counting rules, each bomber is counted as carrying only one warhead even if it is physically capable of carrying more; although the United States would have 1440 ‘accounted’ warheads in this scheme, the actual number could be up to about 1800. These limits are to be accomplished within seven years after the treaty enters into force, which occurred in February, 2011. At the time of writing, less than a year remains until these limits are to be reached. While there is no reason to believe that this will not be the case, the recent rise in east/west tensions has so far precluded any follow-on negotiations.
Table 7.4. Estimated nuclear arsenals in 2010 and after the New START reductions. Numbers are deployed warheads under New START counting rules. Data from [15].
The numbers in table 7.4 appear to give the United States an advantage, but they do not account for Russia’s significant advantage in numbers of tactical weapons, which no treaty has yet addressed.
As the numbers of American and Russian weapons continues to decline, other complications will come into play. At what point do other countries need to be brought into the negotiations, and with whom will America and Russia accept parity? Will countries be willing to accept more intrusive inspections designed to prevent cheating? What do military strategists see as the role of nuclear weapons in a world more concerned with rogue terrorism than the possibility of large-scale wars? Even high-level officers have acknowledged the declining importance of nuclear forces in the post-Cold-War world. In May, 2012, General James E Cartwright, a former Vice-Chairman of the Joint Chiefs of Staff and commander of the United States Nuclear Forces, remarked in the New York Times that the United States’ nuclear deterrence could be guaranteed with a total arsenal of 900 warheads, with only half of them deployed at any one time. As Cartwright wrote, ‘The world has changed, but the current arsenal carries the baggage of the cold war. There is the baggage of significant numbers in reserve. There is the baggage of a nuclear stockpile beyond our needs. What is it we’re really trying to deter? Our current arsenal does not address the threats of the 21st century’. For students interested in arms-control and non-proliferation policies, plenty of work remains to be done.
7.3 Final thoughts
The world’s arsenals of nuclear weapons are the most obvious legacy of the Manhattan Pro
ject, but there are many others. It is no exaggeration to say that the Project turned the course of history, and completely changed the relationship between science and society. Before World War II, annual federal funding for research in the United States was measured in the millions of dollars; it now runs into the tens of billions of dollars to support organizations such as the Office of Naval Research, the National Science Foundation, NASA, the Environmental Protection Agency, the Defense Advanced Research Projects Agency, and numerous national laboratories such as Los Alamos. Many of the scientists who were involved in the Manhattan Project went on to distinguished careers, mentoring numerous students and developing technological innovations that underlie modern electronic devices, computers, defense technologies, and medical treatments.
Nuclear weapons will be with us for decades to come; they cannot be un-invented. They have immense political influence. Military budgets, defense strategies, force deployments, bureaucracies, defense pacts between nations, and thousands of government and contractor employees are involved. Once established, such systems take on lives of their own, and can persist for decades even after events have rendered their original missions irrelevant. Bureaucratic inertia can be just as powerful as nuclear energy.
Fortunately, significant efforts are now being made to preserve some sites and structures associated with the Manhattan Project. In 2003, Congress requested the Department of Energy (DoE) to develop a plan for preserving Project sites. Under an agreement with DoE, the Atomic Heritage Foundation of Washington, DC, took on this task. In 2004, the AHF released a report recommending a Manhattan Project National Historical Park comprising properties located at Los Alamos, Oak Ridge, and Hanford. In September, 2004, Congress passed the Manhattan Project National Historical Park Study Act, which authorized the National Park Service (NPS) to study whether to create such a park. In July, 2011, the NPS and the DoE submitted joint recommendations to Congress for a park with units at the sites indicated above. The Manhattan Project National Historical Park Act (MPNHPA) was introduced in Congress in 2012, and on June 14, 2013, the House of Representatives voted to include it as an amendment to the 2014 National Defense Authorization Act (NDAA). The Senate dropped this amendment, but it was reintroduced in the Fiscal Year 2015 NDAA put forth in April, 2014. The House of Representatives passed this bill on December 5, 2014, by a vote of 300–119; the Senate followed one week later by a vote of 89–11, and President Barack Obama signed it into law one week after that [16].
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