Executive Summary

• The U.S.-Russia Strategic Stability Dialogue, agreed by presidents Joseph Biden and Vladimir Putin at their June 2021 summit, has begun. It presumably is addressing the range of issues affecting strategic stability, including reductions in and limits on strategic offensive nuclear forces as well as questions related to missile defense. 
• Three phases have defined the history of missile defense: the era of unrestrained offense-defense competition prior to the negotiation of the 1972 Anti-Ballistic Missile (ABM) Treaty; the period of arms control between 1972 and 2002, during which both defenses and strategic offensive forces were limited; and the current era of unrestrained defenses and controlled strategic offensive forces, from 2002 to the present. 
• After more than six decades of missile defense investments, strategic offensive forces retain a significant and enduring edge over defensive systems. While progress has been made in defending against shorter-range ballistic missiles and their warheads (which travel at considerably lower velocities than strategic ballistic missile warheads), at no point during any of the three periods has the United States or the Soviet Union/Russia been able to produce a defensive system that has held any short- or medium-term prospect of negating the strategic offensive forces of the other, either on its own or in combination with a counterforce first strike.
• The concerted effort since 2002 by Washington and NATO to develop their missile defense capabilities against the long-range ballistic missile threats posed by North Korea and Iran has enjoyed only limited success, and the viability of the U.S. homeland defense against Pyongyang’s relatively small and unsophisticated nuclear arsenal is still doubtful. Russia’s incremental improvements to its defensive system around Moscow do not pose a significant threat to the U.S. strategic nuclear capability. 
• Nevertheless, the prospect of longer-term improvements to U.S. and Russian missile defenses continues to be a source of uncertainty that exercises considerable influence on the force sizing and development of new capabilities, particularly for Russia and the European nuclear powers, France and the United Kingdom. The limited available evidence suggests that China shares similar concerns regarding the viability of its deterrent against new defensive systems. Russian and Chinese planners appear to fear a future U.S. counterforce attack conducted primarily, or even solely, with advanced, high-precision conventional weapons that would disable a major portion of their strategic forces, leaving the remainder to have to penetrate U.S. missile defenses. 
• For Russia, the prospective long-term threat to its forces posed by the improvement in U.S. defenses and nuclear and conventional counterforce capabilities has prompted it to develop new “exotic” systems designed to ensure its retaliatory capacity, including the Avangard boostglide vehicle, the Poseidon long-range nuclear uncrewed underwater vehicle (UUV) and the Burevestnik nuclearpowered cruise missile. Russia has also expressed significant reservations about further cuts to its strategic offensive forces through arms control, if missile defenses remain unconstrained.
• France and the United Kingdom have been historically far more sensitive to developments in the Moscow ABM system given their smaller and less technologically advanced nuclear arsenals. Both powers have continued to ensure the long-term viability of their deterrents against prospective Russian improvements through the introduction of improved warheads (France) and planned increases in maximum stockpile size (UK).
• China’s smaller arsenal means that Beijing may be even more sensitive to developments in U.S. missile defense policy than Moscow. China’s recent apparent expansion of the number of its intercontinental ballistic missile (ICBM) silos may in part stem from anxieties regarding the viability of its deterrent against prospective U.S. missile defenses, although the motivation for and extent of an expanded ICBM force are still unclear at the time of writing.
• Thus, the current era of unrestrained missile defenses since 2002 has seen the deployment of defensive systems of limited short- and medium-term technical potential, combined with considerable anxiety from four of the five recognized nuclear powers that longer-term technological developments may pose a risk to their forces, stimulating their qualitative and quantitative augmentation. This has resulted in a paradox: even as they remain broadly ineffective against all but the most limited threats, strategic missile defenses nevertheless exert a destabilizing influence on the global nuclear balance.¹ 
• A number of measures, primarily between the United States and Russia, could help to limit the uncertainty over future missile defense capabilities by placing more explicit restraints on today’s limited missile defenses so that they cannot expand into systems that could put the retaliatory capability of any of the five nuclear powers at risk.
• These steps could include confidencebuilding measures, such as transparency agreements and reciprocal observation of missile defense interceptor tests, a ban on space-based missile defense interceptors, clearer unilateral explications of the extent and limits of both Washington and Moscow’s missile defense plans, as well as negotiated limits on missile defenses on either a legally or politically binding basis.
• Given their long-standing interest in missile defenses designed to counter only limited threats and the risks that an offense-defense competition could pose both to stability in the North Atlantic area and the viability of European members’ nuclear arsenals, U.S. NATO allies should do all they can to support these efforts.

Read the rest at The Deep Cuts Commission