Probability of Tactical Nuclear Weapon Use in a US-Israeli Coalition Conflict with Iran: Assessment as of March 18, 2026

This analysis estimates the probability of tactical nuclear weapon (TNW) use by the US-Israel coalition in the ongoing conflict with Iran, employing a simplified Bayesian odds model with multiplicative OR multipliers for identified input variables. The baseline prior (3% at week 6) is combined with seven structural factors - including interceptor depletion, diversionary escalation, China/Russia signaling, and the Taiwan threat - yielding a raw estimate of 57%, subsequently revised to a realistic range of 25-55% (midpoint ~40%) after sensitivity analysis and red team review. The assessment identifies escalation mechanisms, trigger scenarios, falsification conditions with a verification schedule, and cascade effects including conditional probabilities of Russian tactical nuclear use in Ukraine (30-50%) and a full nuclear war chain (1-4%). Inhibiting factors are analyzed qualitatively as binary conditions rather than continuous modifiers. The document concludes that even conservative estimates place the risk at levels comparable to the 1962 Cuban Missile Crisis, and that the scenario cannot be dismissed as improbable. The primary value of the analysis lies in identifying variables, mechanisms, and update indicators rather than in specific percentages. This report constitutes an operational supplement to the War-Peace Validator module of the Triptych framework (DOI: 10.5281/zenodo.17219502).This report was originally written in Polish; the English version is a translation.