The following is the Feb. 2, 2023, Congressional Research Service report, Defense Primer: Strategic Nuclear Forces.
From the report
The Nuclear Triad
Since the early 1960s, the United States has maintained a “triad” of strategic nuclear delivery vehicles. These include long-range land-based intercontinental ballistic missiles (ICBMs), long-range submarine-launched ballistic missiles (SLBMs), and long-range heavy bombers equipped to carry nuclear-armed cruise missiles and gravity bombs. The number of nuclear warheads carried on these delivery vehicles peaked in the late 1980s, at around 14,000 warheads. It has been declining ever since, both as the United States complies with limits in U.S.-Russian arms control agreements and as it has changed requirements after the Cold War. As of February 2018, the United States had reduced its forces to comply with the New START Treaty, which entered into force in early 2011. Table 1 displays the U.S. forces that counted under the treaty limits, as of September 1, 2020. These forces fall below the treaty limits of 1,550 deployed warheads on 700 deployed missiles due to maintenance schedules and operational requirements. According to a January 2023 report to Congress, the United States had 1,420 warheads deployed on 659 missiles and bombers, as of September 1, 2022.
Rationale for the Triad
Early in the Cold War, the United States developed these three types of nuclear delivery vehicles, in large part because each of the military services wanted to play a role in the U.S. nuclear arsenal. However, during the 1960s and 1970s, analysts developed a more reasoned rationale for the nuclear triad. They argued that these different basing modes had complementary strengths and weaknesses that would enhance deterrence and discourage a Soviet first strike. For example, ICBMs were believed to have the accuracy and prompt responsiveness needed to attack hardened targets such as Soviet command posts and ICBM silos, SLBMs had the survivability needed to complicate Soviet efforts to launch a disarming first strike and to retaliate if such an attack were attempted, and heavy bombers could be dispersed quickly and launched to enhance their survivability, and they could be recalled to their bases if a crisis did not escalate into conflict.
The United States has reaffirmed the value of the nuclear triad. The Obama Administration noted, in the 2010 Nuclear Posture Review (NPR), that the unique characteristics of each leg of the triad were important to the goal of maintaining strategic stability at reduced numbers of warheads. It pointed out that strategic nuclear submarines (SSBNs) are the most survivable leg of the triad, that single-warhead ICBMs contribute to stability and are not vulnerable to air defenses, and that bombers can be deployed as a signal in crisis, to strengthen deterrence and provide assurances to allies and partners. It also noted that “retaining sufficient force structure in each leg to allow the ability to hedge effectively by shifting weight from one Triad leg to another if necessary due to unexpected technological problems or operational vulnerabilities.”
The Trump Administration also reaffirmed the U.S. commitment to the nuclear triad and to the modernization programs for each of the components of that force structure. The 2018 NPR notes that “the triad’s synergy and overlapping attributes help ensure the enduring survivability of our deterrence capabilities against attack and our capacity to hold a range of adversary targets at risk throughout a crisis or conflict. Eliminating any leg of the triad would greatly ease adversary attack planning and allow an adversary to concentrate resources and attention on defeating the remaining two legs.” The Biden Administration’s 2022 NPR supports continuing investments in the modernization programs for all three legs of the triad.
Current Forces and Modernization Plans
The United States is recapitalizing each leg of its nuclear triad and refurbishing many of the warheads carried by those systems.
Before implementing the New START Treaty, the United States deployed 450 Minuteman III ICBMs at three Air Force bases: F.E. Warren AFB in Wyoming, Malmstrom AFB in Montana, and Minot AFB in North Dakota. Under New START, the number has declined to 400 deployed missiles, although the Air Force has retained all 450 silo launchers. While each Minuteman III missile originally carried three warheads, each now carries a single warhead, both to reduce U.S. forces to New START levels and to adopt what is considered a more stabilizing posture.
The Air Force has completed several programs designed to improve the accuracy and reliability of the Minuteman fleet and to “support the operational capability … through 2030.” The Air Force is also developing a new ICBM, the Ground-
based Strategic Deterrent (GBSD), which will replace all missiles and ground launch control facilities. It plans to acquire 642 missiles to support testing and the deployment of a force of 400 missiles. The Air Force expects the program to reach its initial operational capacity, with 9 missiles on alert, by 2029; it expects to complete the deployment, with 400 missiles on alert, in 2036. The Biden Administration has included $3.6 billion for the program in its FY2023 budget request.
The National Nuclear Security Administration (NNSA), a semi-autonomous agency in the Department of Energy, is working on a new warhead—known as the W87-1—that will deploy on the new GBSD missile.
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