Nuclear Deterrence in the Beibu Gulf in a Three-Dimensional Framework: Model Development, Strategic Logic, and Empirical Comparison

The South China Sea, as one of the most important maritime corridors in the world, has become a frontier zone for the games of great powers. Beibu Gulf, located at the northern edge of the South China Sea, is both a strategic gateway to China's southern depth and a vulnerable link for potential external forces to intervene. How to establish a credible, controllable and retractable deterrence system within the limited depth has become a major issue in China's strategic research. In this paper, through the method of "four-step mapping model development", the deterrence system in Beibu Gulf is constructed as a three-dimensional framework of "nuclear threshold-conventional denial-time advancement": the inner red ball represents the extreme deterrence threshold, and the inner red ball represents the extreme deterrence threshold, and the inner red ball represents the extreme deterrence threshold, and the outer red ball represents the extreme deterrence threshold. The inner red ball represents the threshold of nuclear deterrence under extreme circumstances, the outer grey ball represents the conventional A2/AD denial zone, and the blue T0-T5 marks the entry path and risk evolution of the opponent's carrier group. This paper innovatively proposes the Deterrence Efficiency Index (DEI) and Escalation Risk Index (ERI) to make the framework computable and verifiable. Using historical comparisons of the Cold War U.S.-Soviet submarine confrontation and the Cuban Missile Crisis, as well as contemporary FONOPs, EDCA extensions, and OSINT data proxies, this study reveals that outer-circle denial can significantly escalate an adversary's costs at the T3-T4 stage, preventing the situation from crossing the nuclear threshold. Nuclear deterrence should therefore be positioned as an "existential penalty" rather than tactical use. It is concluded that the framework bridges the gap between nuclear deterrence and A2/AD research, and provides a scientific framework for policy formulation, crisis management and academic research.