	Introduction

During the Cold War, the U.S. nuclear arsenal contained many types of delivery vehicles for nuclear weapons, including short-range missiles and artillery for use on the battlefield, medium-range missiles and aircraft that could strike targets beyond the theater of battle, short- and medium-range systems based on surface ships, long-range missiles based on U.S. territory and submarines, and heavy bombers that could threaten Soviet targets from their bases in the United States. The long-range missiles and heavy bombers are known as strategic nuclear delivery vehicles. The report not only reaffirms the basic contours of the current U.S. force structure and the ongoing modernization programs, it also calls for the development of a new low-yield warhead for deployment on Trident II (D-5) missiles. This report reviews the ongoing programs that will affect the expected size and shape of the U.S. strategic nuclear force structure. Current and Future Force Structure and Size

The Obama Administration indicated in the 2010 NPR that the United States would retain a triad of ICBMs, SLBMs, and heavy bombers as the United States reduced its forces to the limits in the 2010 New START Treaty. The Trump Administration has continued to adjust the U.S. nuclear force to meet this planned force structure. However, with the signing of the New START Treaty in 2010, these silos added to the U.S. total of nondeployed ICBM launchers. 5122 , §139), Congress stated that DOD could not spend any money to begin the withdrawal of these missiles from the active force until the Secretary of Defense submitted a report that addressed a number of issues, including (1) a detailed justification for the proposal to reduce the force from 500 to 450 missiles; (2) a detailed analysis of the strategic ramifications of continuing to equip a portion of the force with multiple independent warheads rather than single warheads; (3) an assessment of the test assets and spares required to maintain a force of 500 missiles and a force of 450 missiles through 2030; (4) an assessment of whether halting upgrades to the missiles withdrawn from the deployed force would compromise their ability to serve as test assets; and (5) a description of the plan for extending the life of the Minuteman III missile force beyond FY2030. The 2018 Nuclear Posture Review reaffirmed this deployment, with each Minuteman III missile deployed with one warhead under the New START Treaty. Submarine Launched Ballistic Missiles

The U.S. fleet of ballistic missile submarines consists of 14 Trident (Ohio-class) submarines, each originally equipped to carry 24 Trident missiles. To comply with the launcher limits in New START, each of the submarines can now carry only 20 missiles. All the Trident submarines currently in the U.S. fleet now carry the Trident II missile. Under the terms of the original START Treaty, which was in force from 1994 to 2009, the United States could remove warheads from Trident missiles, and reduce the number listed in the database, a process known as downloading, to comply with the treaty's limit of 6,000 warheads. The Navy is also pursuing a life extension program for the Trident II missiles, so that they will remain capable and reliable throughout the 42-year life of the Trident submarines; they will also serve as the initial missile on the new Columbia class submarine. At the same time, it will continue to support the joint U.S./U.K. This process was completed in 1997 and the B-1 bomber is no longer equipped to carry nuclear weapons. The Air Force is also designing a new tail kit for the B61 bomb. Congress also stated that no funds could be spent to retire any B-52 aircraft until the Secretary of the Air Force submitted a report to Congress that described the Air Force plan for the modernization of the B-52, B-1, and B-2 bomber fleets; how many bombers would be assigned two nuclear and conventional missions if the United States had to execute "two overlapping 'swift defeat' campaigns"; a justification of the cost and projected savings of any reductions to the B-52H bomber aircraft fleet; and the life expectancy of each bomber aircraft to remain in the bomber force structure and the capabilities of the bomber force structure that would be replaced by a new bomber aircraft. Long-Range Standoff (LRSO) Weapons

At the end of the Cold War, the B-52 bomber was equipped to carry both the Air-Launched cruise missile (ALCM) and Advanced Cruise Missile (ACM). It is then planning to replace the ALCM with a new advanced long range standoff (LRSO) cruise missile. The Trump Administration did not directly address questions about the size of the U.S. nuclear arsenal in the 2018 Nuclear Posture Review. It indicated that it would continue to support the implementation of New START, at least through 2021, and that it would continue to pursue the nuclear modernization programs that began during the Obama Administration. Analysts outside government have also questioned the Administration's plans to replace the air-launched cruise missile (ALCM) with the new long-range strike missile (LRSO) in the 2020s.
Even though the United States has reduced the number of warheads deployed on its long-range missiles and bombers, consistent with the terms of the 2010 New START Treaty, it also plans to develop new delivery systems for deployment over the next 10-30 years. The 116th Congress will continue to review these programs, and the funding requested for them, during the annual authorization and appropriations process.
During the Cold War, the U.S. nuclear arsenal contained many types of delivery vehicles for nuclear weapons. The longer-range systems, which included long-range missiles based on U.S. territory, long-range missiles based on submarines, and heavy bombers that could threaten Soviet targets from their bases in the United States, are known as strategic nuclear delivery vehicles. At the end of the Cold War, in 1991, the United States deployed more than 10,000 warheads on these delivery vehicles. With the implementation of New START completed in February 2018, the United States is limited to 1,550 accountable warheads on these delivery vehicles, a restriction that will remain in place at least through 2021, while New START Treaty remains in force.
At the present time, the U.S. land-based ballistic missile force (ICBMs) consists of 400 land-based Minuteman III ICBMs, each deployed with one warhead, spread among a total of 450 operational launchers. This force is consistent with the New START Treaty. The Air Force is also modernizing the Minuteman missiles, replacing and upgrading their rocket motors, guidance systems, and other components, so that they can remain in the force through 2030. It plans to replace the missiles with a new Ground-based Strategic Deterrent around 2029.
The U.S. ballistic missile submarine fleet currently consists of 14 Trident submarines. Each has been modified to carry 20 Trident II (D-5) missiles—a reduction from 24 missiles per submarine—to meet the launcher limits in the New START Treaty. The Navy converted 4 of the original 18 Trident submarines to carry non-nuclear cruise missiles. Nine of the submarines are deployed in the Pacific Ocean and five are in the Atlantic. The Navy also has undertaken efforts to extend the life of the missiles and warheads so that they and the submarines can remain in the fleet past 2020. It is designing a new Columbia class submarine that will replace the existing fleet beginning in 2031.
The U.S. fleet of heavy bombers includes 20 B-2 bombers and 40 nuclear-capable B-52 bombers. The B-1 bomber is no longer equipped for nuclear missions. This fleet of 60 nuclear-capable aircraft is consistent with the U.S. obligations under New START. The Air Force has also begun to retire the nuclear-armed cruise missiles carried by B-52 bombers, leaving only about half the B-52 fleet equipped to carry nuclear weapons. The Air Force plans to procure both a new long-range bomber, known as the B-21, and a new long-range standoff (LRSO) cruise missile during the 2020s. DOE is also modifying and extending the life of the B61 bomb carried on B-2 bombers and fighter aircraft and the W80 warhead for cruise missiles.
The Obama Administration completed a review of the size and structure of the U.S. nuclear force, and a review of U.S. nuclear employment policy, in June 2013. This review advised the force structure that the United States will deploy under the New START Treaty. The Trump Administration completed its review of U.S. nuclear forces in February 2018, and reaffirmed the basic contours of the current U.S. force structure and the ongoing modernization programs. The Trump Administration has also called for the development of a new low-yield warhead for deployment on Trident II (D-5) missiles. Congress will review the Administration's plans for U.S. strategic nuclear forces during the annual authorization and appropriations process, and as it assesses the costs of these plans in the current fiscal environment. This report will be updated as needed.