China's Secret Nuclear Tests

This commentary examines US allegations that China has conducted secret underground nuclear tests - most notably an alleged June 2020 detonation presented with new evidence at the United Nations in February 2026 - and the strategic consequences of such activity. Seismic evidence is not decisive, but Beijing has offered no compelling explanation and has resisted transparency. Because China conducted only about 45 tests by the mid-1990s and relied on more limited diagnostics, it has strong incentives to acquire additional test data to modernize and validate warhead designs. US compliance reports since 2019 have suggested probable clandestine testing by China (and Russia), creating verification challenges and raising the risk that the United States might be politically tempted to resume underground testing - a move that would erode international norms and in practice benefit China and Russia more than Washington. Germany and Europe face constrained options and are limited largely to pushing for greater transparency and confidence-building.

The commentary reviews why states test - signalling, deterrence, safety, performance validation and effects testing - and traces the legal and technical regime that has grown up to constrain testing. It recounts Cold War test totals, the US unilateral moratorium from 1992/1996, and the Comprehensive Nuclear-Test-Ban Treaty framework: broadly adhered-to norms, a zero-yield standard, allowance for subcritical experiments, and a stalemate over entry into force because key states have not ratified. The piece argues preserving the testing taboo is crucial to slowing qualitative advances in nuclear arms and impeding proliferation.