Irreversibility in Nuclear Arms Control: Lessons from the US-Soviet/Russian Arms Control Process

ABSTRACT The United States and Soviet Union/Russian Federation signed several arms control treaties that mandated reductions in their numbers of deployed nuclear weapons. These treaties outlined complex technical procedures that governed the process of eliminating weapons in excess of allowed numbers. The procedures often required the physical destruction of missiles and launchers, thus making it difficult for the parties to reverse the elimination of these weapons while the treaties remained in force. These complex procedures also helped the parties verify compliance, as both the elimination process and the reduction in numbers were required. However, most of the treaties allowed the parties to produce and deploy new weapons while the treaty was in force, as long as the numbers remained within the treaty limits. Moreover, the parties could add to their forces and reverse their reductions after the treaties lapsed. Thus, even if the treaty required irreversible procedures to implement the mandated reductions, the outcome would not necessarily remain irreversible forever. Both parties could restore capabilities if their security assessments changed. Thus, a political commitment to restrain nuclear programs may be more important in ensuring the long-term irreversibility of disarmament than the legal obligations and technical procedures codified in arms control agreements.


Defining, and Describing, Irreversibility
In his paper titled "'Approaching Irreversibility in Global Nuclear Politics", Hassan Elbahtimy states that incorporating irreversibility in arms control would "entail devising technical, legal, political and normative measures that seek to limit the potential for building back weapon systems following disarmament [emphasis added]" (Elbahtimy 2023).Adding context to this basic definition, an arms control agreement mandating the irreversible elimination of a class of weapons -such as nuclear explosive devices -would outline technical implementation procedures that would result in the physical or functional destruction of existing weapons.It would then incorporate these procedures into a legal framework, such as a formal treaty, through which the parties would assume the obligation to eliminate their weapons according to the prescribed technical procedures.When signing the treaty, the parties would reveal their political commitment to eliminate their stock of treaty-limited items and their recognition of normative restraints on the acquisition and possession of such weapons.
Yet, as Elbahtimy notes in his definition, the legally binding procedures and political commitments captured in an arms control agreement would only "limit the potential" for building back the prohibited weapons.They would not necessarily remain irreversible over time.Not only could the parties to the treaty rebuild and restore the weapons if they retained the necessary technology and infrastructure, but they could choose to rescind their political commitment and reject the norms of restraint if they believed they needed new or similar weapons to meet their national security needs in a changing geopolitical environment.
The incorporation of irreversibility into arms control agreements is essentially two separate endeavors -the first would seek to make the technical procedures used to eliminate treaty-limited items difficult or impossible to reverse in the near term, while the second would seek to cement the norms captured by the treaty in the international system so that the parties' political commitments would endure over the long term.The first addresses efforts to limit the potential for reversing the process of implementing the treaty while the second seeks to limit the potential for reversing the outcome of the treaty's implementation.
The concept of irreversibility has become part of the discussion about nuclear disarmament, with many seeking not only political and normative commitments from nations willing to commit to the elimination of nuclear weapons, but also a process that would allow for the physical destruction of those weapons and ensure the durability of that outcome.Even though there are distinct differences between agreements that limit the numbers of warheads deployed on missiles and bombers and those that seek to eliminate all nuclear weapons, the bilateral nuclear arms control treaties signed by the United States, Soviet Union, and Russia can contribute to this discussion.Specifically, some of these bilateral agreements mandated that the parties use detailed technical procedures to eliminate weapons that exceeded the limits in the treaties.These procedures often destroyed the weapons in ways that made it difficult, if not impossible, to reverse their elimination, and, therefore, supported the goal of ensuring that the reductions would be irreversible in the near term.
Yet, treaties negotiated as a part of the US-Soviet and US-Russian arms control process often contained pathways the parties could follow to retain their military capabilities even as they complied with the treaty restrictions.As others have noted, this creates a paradox, where "negotiators often seek to ensure that progress made in nuclear arms control is enduring", while, at the same time, ensuring that they allow the parties the "flexibility to respond to changes in the security environment" (Rodgers and Williams 2023).The treaties have allowed the parties to deploy weapons with similar capabilities without counting them under the treaty limits and to replace aging weapons with new systems as long as the deployed forces remained within the treaty limits.Moreover, while some treaties were of unlimited duration, others expired on a set schedule, and all contained withdrawal clauses.These provisions gave the parties the flexibility to step out from under the limits in response to changes in the security environment.
The bilateral arms control process, therefore, offers examples of cases where it would be difficult for the parties to reverse the process of eliminating their weapons in the near term while leaving open pathways if they wanted to reverse the outcome of the treaty's implementation in the long term.Moreover, these treaties have not been comprehensive enough in the short term or irreversible enough in the long term to prevent the parties from restoring their capabilities if they determined that such a reversal was necessary to meet their national security requirements.As a consequence, the long-term durability of the bilateral arms control process rests more on the parties' political commitment to restrain their nuclear programs than on the legal obligations and technical procedures codified in their arms control agreements.

Scope of the Paper
This paper reviews three arms control treaties signed by the United States, Soviet Union and Russia -the 1987 Intermediate Range Nuclear Forces Treaty (INF), the 1991 Strategic Arms Reduction Treaty (START) and the 2010 New Strategic Arms Reduction Treaty (New START) -to identify ways in which these treaties incorporated irreversibility into their implementation process but left open pathways that allowed the parties to restore their capabilities and reverse the outcome of that implementation.It then identifies lessons about the role of irreversibility in arms control that might be taken from the bilateral arms control process into broader negotiations on nuclear disarmament.
The paper focuses on the provisions in bilateral nuclear arms control agreements because advocates of nuclear disarmament often see the bilateral arms control process as a pathway to disarmament.Therefore, an evaluation of the technical measures designed to ensure the physical elimination of delivery systems for nuclear weapons might not only offer examples for inclusion in disarmament agreements, but also offer insights into how these procedures work to complicate or prevent a reversal of the disarmament process.Moreover, understanding how the United States, Soviet Union, and Russia employed irreversibility in their implementation procedures -by noting when they insisted on a greater degree of irreversibility and examining the circumstances when they were willing to accept less complex and permanent technical procedures -can provide insights about the role of irreversibility in their arms control process.
The analysis in this paper will describe the limitations placed on irreversibility in bilateral arms control agreements and explore the role that flexibility plays in allowing the parties to accept limits on weapons deemed central to their national security needs.While such flexibility might be an anathema to efforts to eliminate all nuclear weapons, it highlights the fact that the long-term durability and irreversibility of disarmament is likely to be as much a function of political commitments in a stable security environment as they are a result of the technical procedures codified in a disarmament agreement.

Intermediate-Range Nuclear Forces Treaty (INF)
The United States and Soviet Union signed the Intermediate Range Nuclear Forces (INF) Treaty in December 1987.It is often hailed as a ground-breaking endeavor because it was the first US-Soviet arms control treaty to ban, rather than limit, an entire category of missiles and the first to incorporate on-site inspections into its monitoring regime.It contained detailed technical measures that incorporated irreversibility into its implementation process, but it still failed to endure over time as political commitments waned and the international security environment changed.
Under the INF Treaty, the United States and Soviet Union agreed to destroy all ground-launched ballistic missiles and ground-launched cruise missiles with a range between 500 and 5,500 kilometers.1This mandate applied to both nuclear-armed missiles and those equipped to carry conventional warheads, but did not extend to the elimination of sea-based or air-delivered missiles with a range within the proscribed parameters.The United States and Russia also agreed to eliminate the launchers, support structures, and support equipment associated with the banned missiles.Further, the Treaty stated that neither party could produce or flight-test any new ground-launched intermediaterange missiles or produce any stages of such missiles or any launchers for such missiles in the future (US Department of State 1987).
The INF Treaty entered into force in late 1988 and was of unlimited duration, although either party could withdraw from the Treaty in response to "extraordinary events" that "jeopardized its supreme interests" (US Department of State 1987).The United States announced its intent to exercise this withdrawal option on 1 February 2019.The United States cited its finding, first announced in 2014, that Russia had violated the Treaty by testing a new cruise missile with a range that was covered under the ban in the Treaty (US Department of State 2014).But it also attributed its decision to concerns about the expanding number of intermediate-range missiles deployed by China and the potential need for the United States to counter these systems by deploying its own intermediate-range missiles in the Indo-Pacific (US Library of Congress, Congressional Research Service 2019).Russia responded by suspending its participation in the INF Treaty on 2 February 2019.The US withdrawal took effect six months later, on 1 August 2019.
The INF Treaty included an Elimination Protocol that outlined the technical measures that were designed to ensure that the parties would find it difficult, if not impossible to reverse the process of eliminating the banned weapons.Specifically, they required that the parties physically destroy all intermediate range missiles in existence when the Treaty entered into force, along with the specialized vehicles used to transport and launch the missiles.These procedures included such steps as cutting launchers, airframes, and other vehicles into two pieces, cutting the wings and tail sections off of cruise missiles, launching ballistic missiles to destruction, and eliminating rocket motors and other components by "explosive demolition or burning" or by crushing or flattening them so that they could not be restored or reused in a missile program (US Department of State 1987).
The INF Treaty also allowed each party to observe the other party's implementation of the elimination procedures, using overhead reconnaissance satellites and on-site inspections.A party's failure to follow the prescribed procedures would violate the Treaty, even if the missiles and equipment were otherwise rendered inoperable.Thus, by collecting evidence of compliance with the required technical measures, the parties could confirm that the elimination was irreversible.Moreover, when combined with the requirement that the parties provide notifications when they moved treaty-limited items between permitted locations, the elimination procedures helped ensure that neither side could remove a significant number of missiles from their deployed forces, conceal them in hidden locations, and possibly return them to the force in violation of the treaty (US Library of Congress, Congressional Research Service 2019).
The technical procedures codified in the Elimination Protocol in the INF Treaty essentially guaranteed that the United States and Soviet Union would not be able to restore and reuse the land-based intermediate-range missiles in existence when the INF treaty entered into force.The process of eliminating these missiles was irreversible.But the treaty's prohibitions on testing and deployment did not extend to all types of intermediate-range missiles, leaving both the United States and Russia with pathways to evade or reverse the outcome of the treaty's implementation in response to changing assessments of their national security requirements.
The INF Treaty did not ban or limit the possession, testing, or production of sea-based or air-delivered intermediate-range ballistic or cruise missiles with a range between 500 and 5,500 kilometers.During the negotiations, the United States had proposed that the Treaty only ban land-based missiles because this was where the United States and its allies had their greatest concerns about the Soviet threat.The United States also wanted to avoid limits on sea-based and air-delivered systems because it had an advantage over the Soviet Union in the numbers and capabilities of these systems.The Soviet Union recognized the US advantages, but essentially agreed to limit the ban in the INF Treaty to land-based missiles with the expectation that the emerging START Treaty would address the threat from sea-based and air-delivered systems.The lack of limits on seabased and air-delivered intermediate-range missiles thus provided the United States with a pathway to maintain intermediate-range missiles while it implemented the INF treaty.
These provisions also provided Russia with a pathway to restore intermediate range missiles after it had completed the required elimination procedures.Specifically, the INF Treaty allowed the parties to test sea-based and air-delivered missiles on land, as long as the test launcher was not mobile, was located at the test site, was different from operational launchers for ground-launched missiles and was used "solely for test purposes" (US Department of State 1987).But the Treaty did not provide the parties with the means to determine whether missiles in their early phases of testing would eventually be deployed at sea or on land, thus providing them with the opportunity to mix landbased missiles into the test program.Moreover, the Treaty imposed no limits on the development of systems with ranges below 500 kilometers and did not describe how the parties would determine the actual range of new missiles if one party assessed them to have a greater range capability in spite of the absence of tests beyond 500 kilometers.
The United States believes Russia took advantage of the absence of clarity in these areas when it began to test the 9M-729 ground-launched cruise missile in 2008.According to US officials, Russia first tested the missile to a range "well over" 500 kilometers from a fixed launcher at a test site, which would be permitted if the missile were to be deployed at sea.But "Russia then tested the same missile at ranges below 500 kilometers from a mobile launcher."Thus, according to US assessments, Russia developed a ground-launched intermediate range missile "by putting the two types of tests together" (Office of the Director of National Intelligence 2018).
Russia denied these claims, stating that the missile was an "upgraded version of the Iskander-M system missile" that was launched to a maximum range of "less than 480 km" (Ministry of Foreign Affairs of the Russian Federation 2018).Russia offered to let the United States inspect the canister for the missile, but refused to demonstrate its range and provided no way for the United States to determine that range independently (Ministry of Foreign Affairs of the Russian Federation 2019).
The decisions leading to the demise of the INF Treaty -including the US withdrawal from the treaty and Russia's suspension of its participation -demonstrate that the technical measures and legal commitments codified in a treaty cannot ensure the longterm durability of that agreement or the irreversibility of its implementation goals if the parties believe their security interests have changed enough to override their political commitment to the treaty's norms and rules.As a result, Russia has not only deployed a land-based missile that the United States believes can fly to an intermediate range but has also employed intermediate-range sea-launched and air-delivered missiles during the conflicts in Syria and Ukraine.The United States not only continued to deploy sea-based and air-delivered cruise missiles after the INF Treaty entered into force, but also might deploy land-based intermediate-range missiles in the Indo-Pacific to address its concerns with security in that region (Ismay 2024).

Strategic Arms Reduction Treaty (START)
The United States and Soviet Union signed the first Strategic Arms Reduction Treaty (START) in July 1991, shortly before the demise of the Soviet Union.2They negotiated this treaty at a time when both parties remained wary of the other's commitment to reducing its numbers of deployed nuclear warheads.As a result, START contained technical implementation measures that were designed to assure each side that the other was completing the required reductions and to complicate efforts to reverse the reductions while the treaty remained in force.But the treaty did not ban the development of new types of systems that would count under its limits.It also was set to lapse after 15 years of implementation, thus providing the parties with pathways to expand their forces and, if they deemed necessary, reverse their reductions.
START entered into force in December 1994 and remained in force through 4 December 2009.The Treaty included a withdrawal clause, but neither party exercised this option, as neither side saw a need to reverse the reductions in their nuclear forces following the end of the Cold War and the subsequent improvements in the US-Russian relationship.The parties could have extended the treaty for five years, through 2014, but they chose to let it lapse while they completed their negotiations on the 2010 New START Treaty.
START permitted the United States and Russia to deploy 1,600 long-range nucleararmed delivery systems, i.e. launchers for land-based and submarine-based long-range missiles (ICBMs and SLBMs, respectively) and heavy bombers equipped to deliver nuclear weapons.It then limited each side to 6,000 warheads on these delivery systems, with no more than 4,900 on ICBMs and SLBMs.The Treaty did not count the warheads directly; it attributed a number of warheads to each type of missile or bomber, then calculated the number of warheads that would count under the Treaty by multiplying this attribution number by the number of deployed missiles and bombers.Thus, to reduce their warheads from the more than 10,000 deployed on each side before the Treaty entered into force to the limits of 4,900 and 6,000, the United States and Russia had to physically destroy the launchers for ICBMs and SLBMs and either physically destroy heavy bombers or convert them so that they could no longer deliver nuclear weapons (US Department of State 1991).
Many of the technical elimination procedures that the parties would use to complete the implementation of START are similar to those in the INF Treaty.They required the crushing, cutting up, or explosive destruction of missile stages, launch canisters, and fixed or mobile launch vehicles for ballistic missiles (US Department of State 1991).As they had in the INF Treaty, these procedures made it difficult, if not impossible, for the parties to reverse the process of eliminating missile launchers so that they no longer counted under the treaty limits.The conversion rules, most of which applied to bombers, were less onerous, but still required that the bombers be rendered incapable of carrying nuclear weapons and that non-nuclear bombers displayed observable differences from bombers that remained a part of the nuclear force.Some of the procedures used to remove the nuclear capability from bombers could be reversed, but their reversal would likely be visible to the parties as they monitored implementation of the treaty provisions (US Department of State 1991).
As had been the case in the INF Treaty, START mandated that the parties conduct these procedures at designated elimination facilities with each side monitoring the destruction process with overhead reconnaissance satellites and on-site inspections.Failure to follow the prescribed procedures would violate the treaty, even if the missiles and equipment were otherwise rendered inoperable.This evidence of compliance with the required technical measures would help each side verify that the other had reduced its numbers of accountable warheads.The elimination procedures also helped ensure that neither side could rapidly restore launchers and warheads to their force, to either evade the limits while the START Treaty remained in force or to exceed the limits after it lapsed.
Unlike the INF Treaty, however, START allowed the parties to produce and deploy new missiles, submarines, and bombers while the Treaty was in force, as long as the numbers of warheads attributed to existing and new systems did not exceed the limits in the Treaty.Moreover, the legal obligation to remain within those limits would lapse when START expired in 2009.Thus, the outcome of START's implementation and the reductions from over 10,000 to under 6,000 deployed warheads was not irreversible.
The international security environment and the political relationship between the United States and Russia changed significantly between 1991, when the United States and Soviet Union signed START, and 2009, when the United States and Russia began their negotiations on the follow-on New START Treaty.Both parties seemed comfortable reducing their numbers of deployed nuclear weapons without entertaining plans to reverse those reductions, even though they could have done so after START expired.The technical measures they used to eliminate weapons in excess of those permitted by the treaty gave each confidence in the other's compliance with the treaty, but it was their political and security assessments, rather than the technical measures, that fostered the durability of those reductions.
The US and Russian political commitment to the arms control process was also evident while START remained in force as they negotiated two other nuclear arms control treaties between 1993 and 2003.The 1993 START II Treaty, which was negotiated shortly after the collapse of the Soviet Union but never entered into force, would have required that the parties reduce their numbers of deployed warheads from the 6,000 permitted under START to between 3,000 and 3,300 warheads.It also would have used technical measures similar to those in START to govern the process of eliminating launchers, and therefore, removing warheads from accountability.Therefore, it would have achieved a measure of irreversibility in the reductions process.At the same time, the parties could have modernized their nuclear delivery systems while the treaty remained in force and restored warheads to their deployed forces after it lapsed in 2003, thus providing a possible pathway for the parties to eventually reverse their reductions if they deemed it necessary.
The 2003 Strategic Offensive Reductions Treaty, often referred to as the Moscow Treaty or SORT, also called for deeper reductions in operationally deployed warheads, to between 1,700 and 2,200 warheads, but did not contain any elimination rules or procedures and did not require that either side implement irreversible reductions in their numbers of nuclear weapons.Each side could simply declare how many warheads it deployed at the conclusion of the Treaty's implementation, without providing any evidence to support the declaration.Moreover, the Treaty would have expired at the deadline given for the parties to reduce their weapons, thus allowing them to reverse the reductions as soon as they were complete.This was by design, as the United States insisted on maintaining the flexibility to restore its forces if it needed to address future security concerns (US Library of Congress, Congressional Research Service 2011).
While the Moscow Treaty was set to expire on 31 December 2012, it lapsed on 5 February 2011, when New START entered into force.Thus, the United States never had the opportunity to exercise its right to exceed the treaty's limits.Because the limits negotiated for New START were even lower than those in the Moscow Treaty, it seems unlikely that either party would have found a reason to reverse their reductions in 2012.At that time, the international security environment and the state of the US-Russian relationship both supported a continuing political commitment to restraint in the numbers of deployed nuclear warheads.

New START
Early in his first term, President Barack Obama pledged to pursue negotiations on a treaty that would replace the original START Treaty with verifiable, legally binding limits (Obama 2009).The United States and Russia signed New START in April 2010.It entered into force in February 2011 and, after Presidents Biden and Putin agreed to a 5-year extension, was scheduled to remain in force through February 4, 2026. 3hile crafted as a follow-on to the expiring START Treaty, New START took a somewhat different approach to the balance between irreversibility and flexibility.It included some of the same technical measures that governed the eliminations process in prior treaties, but relaxed others, thus making it less onerous for the parties to eliminate treaty-limited items and remove them from accountability.Yet, this would also make it easier for them to reverse some of the results of the elimination process after the treaty lapsed.
Under New START each side could deploy a maximum of 700 long-range missiles and heavy bombers, within a total of 800 deployed and nondeployed missiles and bombers.The Treaty also limited each side to no more than 1,550 warheads on deployed launchers; that total counts the actual number of warheads deployed on ICBMs and SLBMs, and one warhead for each deployed heavy bomber.As was the case in START, missiles and bombers, along with the warheads they carry, count under the Treaty's limits until they are either converted or eliminated according to the procedures described in the Treaty's Protocol.A failure to follow the prescribed procedures would violate the Treaty, even if the systems were otherwise rendered inoperable (US Department of State 2010).
At the same time, New START provided the United States and Russia with more options for procedures to eliminate their excess weapons than had the original START Treaty.For example, under START, the parties had to eliminate ICBM silos -the buried concrete structures used to launch land-based missiles -by either digging them out of the ground "to a depth of no less than eight meters" or by blowing them up "to a depth of no less than six meters" (US Department of State 1991).After implementing these procedures, the silos could no longer launch missiles and repairing them would take as much, if not more time than building new silos.New START added a third elimination procedure; the United States and Russia could eliminate the silos by filling them "completely with debris resulting from demolition of infrastructure, and with earth or gravel" (US State Department 2010, 93).While it would be difficult to remove the gravel and restore the silos, this procedure did not mandate the physical elimination of the structure and, therefore, might have been easier to reverse without building new silos.The United States used this procedure, filling 50 silos in Montana with gravel, to reduce its numbers of treaty-accountable launchers.The Treaty also permitted the parties to use "other procedures that are developed by the Party carrying out the elimination".There was no requirement that these "other procedures" be irreversible, or even that they damage or destroy the silo's structure (US State Department 2010).
New START also relaxed the provisions governing the elimination of launchers from ballistic missile submarines.Under the original START Treaty, if the parties did not eliminate the entire submarine, they would have had to physically remove the entire missile section or remove the missile launch tubes and "all elements of their reinforcement, including hull liners and segments of circular structural members between the missile launch tubes, as well as the entire portion of the pressure hull, the entire portion of the outer hull, and the entire portion of the superstructure through which all the missile launch tubes pass" (US State Department 1991).While these procedures may have allowed the parties to use the submarines for other purposes, they would have required extensive modifications at a high financial cost to achieve that goal.Thus, neither side pursued these options.
New START, in contrast, allowed the parties to reduce the number of launch tubes that counted on a submarine without cutting out the entire missile compartment or the missile launch tubes.They could, instead, convert launch tubes by reducing the "height or diameter of the launcher" so it could no longer contain an SLBM or removing "critical components required to launch an SLBM".According to the Treaty's Protocol, the party using these procedures had to permit the other party to inspect the submarines to "confirm that the procedures . . .have been completed".But the inspecting party did not have the right to object to the procedures or to insist that they be irreversible, as long as they were completed in a way that precluded their use as an SLBM launcher (US State Department 2010, 95-96).
The United States used this procedure to reduce its number of launch tubes that would count on each of its ballistic missile submarines; it installed steel plates that shorten four of the 24 launchers on each submarine, leaving only 20 to count under the Treaty.Russian officials have insisted that this procedure is not sufficient, both because the United States could remove the steel plates and reverse the conversion, and because Russia cannot confirm that the launch tubes are incapable of launching ballistic missiles unless they inspect inside the tubes.The United States rejected Russia's complaint because the Treaty permitted an inspection only to confirm that the procedure -in this case, the installation of a steel plate -is complete, and precisely because the Treaty does not mandate that the reductions be irreversible (US Library of Congress, Congressional Research Service 2022).
Several factors allowed the United States and Russia to relax their elimination procedures under New START.First, they had negotiated the more complex and comprehensive procedures in the original START Treaty during the 1980s, when their political relationship remained fraught.Neither was certain the other would comply with the Treaty; the United States, in particular, sought added assurances that it would be able to detect evidence of Soviet violations (US Library of Congress, Congressional Research Service 2011).The irreversibility of the technical measures, when combined with the ability to monitor their implementation, helped each side confirm that the other party had eliminated, and not hidden, excess missiles.Second, as the two parties acquired experience during the implementation of START, they recognized that some of the mandated procedures were more comprehensive than needed to ensure that the launchers could not be returned to operational status.They also recognized that these procedures imposed high financial and technical burdens.Thus, as their political relationship improved and their confidence in the other side's commitment to the Treaty expanded, they recognized that less rigorous measures would be sufficient (Gottemoeller 2020).
The changes in the procedures for eliminating SLBM launchers also served the US interests by providing it with the flexibility to sustain its preferred force structure and possibly return converted submarine launch tubes to service.The United States negotiated these procedures precisely because they could be reversed.The United States maintains a force of 14 Ohio-class ballistic missile submarines with 24 launch tubes on each submarine.If it had to use the elimination procedures mandated by START to comply with the reductions in New START, it would have had to either reduce the size of its submarine force or eliminate a significant number of its ICBM silos.By reducing the number of launchers counting on each submarine, it could avoid that trade-off and retain its existing force posture and deployment patterns.Moreover, if security conditions changed during or after the implementation of New START, the United States could restore missiles and warheads to these submarines to meet a potential change in requirements.
The differences between the elimination protocols in START and New START demonstrate that efforts to incorporate irreversibility in arms control must be measured not only by the rigor of the technical mechanisms, but also by the tenor of the political relationship.The United States and Russia relaxed the elimination procedures in New START in response to both their shared experience of implementing START and their confidence that neither side would seek to rebuild its forces while the treaty remained in force.Thus, their shared commitment to the arms control process was as important to restraining their forces as the technical measures governing the elimination of excess weapons.
Russia suspended its implementation of New START in February 2023, cutting off the notifications, data exchanges, and inspections that helped each side verify compliance with the treaty; the United States followed suit in March 2023 (US Department of State 2023a, 2023b).Both sides have pledged to observe the treaty limits through 2026, but this restraint can be reversed.Because each side could reduce its numbers of accountable warheads without eliminating the launchers, each side can add to these numbers by restoring warheads to existing delivery systems.The United States could also restore converted launch tubes on ballistic missile submarines.And both could eventually build new delivery systems to expand their numbers of deployed warheads.More rigorous elimination procedures might have made it more difficult to reverse these reductions, but they would not have prevented a collapse of political support for arms control.

Lessons for Future Disarmament Agreements
This paper's review of the use of irreversibility as an implementation tool in bilateral nuclear arms control treaties presents several potential lessons for future disarmament agreements.The first of these is the recognition that the legal obligations to use irreversible procedures when implementing a treaty cannot ensure that the outcome of that implementation will remain irreversible forever.Most treaties have expiration dates and withdrawal clauses, so the legal framework will only persist as long as the parties retain their political commitment to restraint.And most treaties are unlikely to apply broadly enough across the participants' technical and industrial infrastructure to eliminate all pathways to the development of new weapons capabilities.This would be particularly true for nuclear disarmament because nations are likely to use the same facilities to disassemble their weapons as they used to assemble them, as the process is highly sensitive and specialized. 4As long as the facilities remain in operation, they could provide a pathway to reverse reductions and recreate a small stockpile of operational warheads.
Second, the technical measures used to impose irreversibility during implementation are designed to make reversal complicated and easy to detect if attempted.Extending those technical measures to include more of the supporting infrastructure for nuclear weapons and, possibly, facilities that support other types of military capabilities or technologies can make it more difficult and lengthen the time to reversal.But the parties to the treaty may leave similar capabilities outside the legal framework of the treaty and may leave open some pathways to reversal if they believe these capabilities are necessary to meet their national security requirements or to support other economic interests.Thus, the parties could conclude that extending the reach of the treaty to slow or block pathways to reversal could impose unacceptable risks for the parties' national security or economic interests.
Third, the technical measures that the parties require and accept during treaty negotiations can vary, with a number of factors affecting their willingness to incorporate irreversibility into the treaty's implementation.A lack of confidence in the other party's commitment to the treaty can bolster support for more rigorous measures to build confidence and demonstrate commitment.On the other hand, the complexity of the elimination procedures and the burden they impose on military operations by taking manpower and funding away from other priorities can lessen demands for irreversible procedures.Moreover, confidence gained over time, as the parties negotiate and implement subsequent treaties, can reduce the demand for complex procedures.And one or both parties may want to retain the flexibility to reverse reductions after the treaty expires or if international security conditions change.Thus, decisions on how much irreversibility to include in a treaty's legal structure can reflect a relative balance of demands and interests, rather than an absolute intention to prevent the reversal of the treaty's obligations.
Finally, in the US-Soviet and US-Russian arms control experience, the provisions in the treaties reflected the state of the political relationship -when each party's confidence in the other party's commitment to arms control was low, the incentives to incorporate irreversibility in a treaty's elimination procedures were high.As confidence in the political commitment increased, the incentives to include more complex procedures declined.But the state of the political relationship can change.During the 1990s and 2000s, the United States and Russia reduced their forces well below the limits in the original START Treaty in response to a changing security environment.They did not need the complex elimination procedures required by the treaty to guide that process.In contrast, the breakdown in the US-Russian relationship during the implementation of New START might have spurred a reversal of that treaty's reductions even if the treaty had included more rigorous elimination procedures.
Thus, the parties' political commitment to restrain their nuclear programs may be more important in ensuring long-term irreversibility than their legal obligations to implement specified technical procedures.It may, therefore, be as important for the parties to accept irreversible disarmament as a political goal as it is for them to implement irreversible elimination procedures in formal, legally binding agreements.The legal obligations can bolster confidence in the completion of the procedures.But, without political commitments, the legal obligations may be neither durable nor irreversible in the long term.