The Defense Department’s annual report on China’s military power assessed that its nuclear arsenal could quadruple by 2030. Last week’s report also confirmed that China is building three missile-silo fields, which analysts expect to account for a significant increase in the projected warhead stockpile.

China is modernizing, diversifying and expanding its nuclear forces. As James Cameron recently explained here at TMC, over the summer China also reportedly tested an orbital bombardment system with a hypersonic glider vehicle.

Why are these developments happening now, and what do they mean for U.S.-China relations?

China may be expanding its options

The most likely reason behind China’s changing nuclear force structure reflects Beijing’s attempts to remove any doubts in the minds of other nuclear powers that it can retaliate for a nuclear attack, especially in the face of U.S. nuclear modernization plans.

Historically, China has maintained a relatively small nuclear force with 200 or so operational warheads, perhaps half of which are mounted atop delivery systems capable of reaching the United States. China’s nuclear strategy of assured retaliation aimed to deter nuclear threats or attacks — and ensure that China could retaliate if it came under nuclear attack.

China has long worried about the survivability of its small force for two main reasons. The first is U.S. offensive nuclear capabilities, which give it the ability to find and attack China’s nuclear forces.

The second relates to U.S. missile defenses, particularly after Washington withdrew from the Anti-Ballistic Missile Treaty in 2002. Although some analysts doubt the U.S. ability to shoot down missiles fired at the U.S. homeland, our research found that Chinese experts worry that U.S. defenses could diminish China’s ability to retaliate if the United States attacks it with nuclear weapons.

Chinese experts have been watching for signs of growing U.S. missile defense ambitions, like the recommendation in the Pentagon’s 2019 Ballistic Missile Defense Review that the United States explore boost-phase and space-based missile defenses. And the United States tested an SM-3 interceptor against an intercontinental ballistic missile, or ICBM. Previous U.S. policy called for the SM-3 to intercept shorter-range missiles only.

A larger nuclear arsenal, kept at a higher state of readiness, would leave China better equipped to deter any nuclear attack its adversaries might be tempted to initiate. And capabilities like the one China reportedly tested this summer could help Chinese weapons overcome new missile defenses — a reminder to the United States that missile defenses can trigger counter-innovations.

A potential conflict over Taiwan raises the stakes

The free fall in U.S.-China relations since 2020, many experts agree, raises the likelihood of a crisis or conflict involving nuclear use by either country. As the conventional (nonnuclear) military balance in East Asia continues to tip in China’s favor, one big question is whether the United States would face stronger temptations to threaten nuclear use as a way of deterring China from using force against Taiwan.

For example, this year’s Pentagon report indicated that Chinese analysts worry the United States could use low-yield nuclear weapons against a Chinese fleet en route to invade Taiwan. That temptation might be even stronger if U.S. nuclear weapons and missile defenses together could seriously limit China’s ability to retaliate.

In this light, a larger nuclear arsenal might boost China’s chances of deterring the United States from any kind of nuclear use — but also increase China’s confidence about deploying its conventional capabilities. This is what scholars call the “stability-instability” paradox: When adversaries worry less about a conflict going nuclear because their nuclear arsenals are stalemated, they’re more likely to start nonnuclear conflicts.

Our earlier research has showed that Chinese experts appeared confident that a U.S.-China conflict wouldn’t go nuclear. But the rapid deterioration of political relations with the United States has almost certainly shaken that confidence. Chinese analysts also perceived that aspects of the 2018 U.S. Nuclear Posture Review Report lowered the threshold for nuclear use. Developing a larger and more sophisticated Chinese arsenal, however, could restore some of that confidence.

What’s next?

While any potential changes in Beijing’s nuclear strategy are unclear, three questions stand out regarding how Beijing might seek to use silo-based missiles to deter the United States. Would Beijing engage in a “shell game,” in which only some silos were loaded with armed missiles, or would it fill all silos with missiles? Would Beijing plan to keep missiles mated with warheads in these silos? And would it keep missiles on high alert, to launch in the event China receives warning of an incoming attack?

For U.S. planners, the projected expansion of China’s arsenal is yet another sign of deepening and destabilizing military-technological competition with the United States. Nevertheless, neither the Chinese military or the Pentagon report say much about the goals of China’s nuclear strategy — and whether the goals of that strategy are expanding to include nuclear first-use. The Chinese government has not publicly acknowledged the construction of the silo fields or provided any information about the current or future size of its force.

Two shifts in China’s nuclear thinking may be happening. First, Chinese leaders believe that they now need to threaten the United States with greater nuclear damage to deter a U.S. nuclear first-strike: a handful of warheads is no longer enough.

Second, China’s leaders may be finding Beijing’s promises not to engage in a nuclear arms race increasingly difficult to fulfill — or less of a priority than deterring U.S. nuclear use with more confidence. But even if the Chinese arsenal does quadruple by 2030, it would still be roughly one-third the size of the U.S. stockpile of 3,750 warheads.

China’s expanding arsenal will pose challenges to the U.S. nuclear posture, forcing the U.S. to plan to deter both Russia’s and now China’s large and sophisticated arsenal. How this new nuclear environment affects U.S. nuclear modernization plans and future strategic arms control with Russia will depend on whether planners decide the U.S. could face major conflicts with both rivals at once or in quick succession. And how U.S. allies view the credibility of its extended nuclear deterrence guarantees will also be a factor.

Alternatively, the U.S. and China could try arms control. Yet there are few promising signs that either country has the political appetite to discuss their nuclear weapons at all, let alone limits on capabilities.

Fiona Cunningham (@Fiona_Cunning) is assistant professor of political science at the University of Pennsylvania and a nonresident scholar in the Nuclear Policy Program at the Carnegie Endowment for International Peace.

M. Taylor Fravel (@fravel) is Arthur and Ruth Sloan Professor in the Department of Political Science and director of the Security Studies Program at the Massachusetts Institute of Technology.