<p>Chaff, consisting of metal-coated fibers, is used as a countermeasure against guided missiles and enemy attacks. To analyze the dynamic behavior of naval chaff dispersed by blasts, we established a numerical framework that couples computational fluid dynamics with the discrete element method. Numerous chaff fibers, represented as slender cylinders, were subjected to blast pressure and airflow calculated by computational fluid dynamics. Additionally, their motions were determined by the discrete element method considering collisions. A blast model, used to set initial conditions in the computational fluid dynamics simulations, was formulated based on the energy conservation of an ideal gas and validated through comparison with other models and sensitivity analysis of the blast temperature. Using the established framework, we simulated the spatiotemporal dispersion process of chaff, categorizing it into blast-driven, transition, and gravity-driven phases. Additionally, we investigated the influence of the chaff cartridge orientation at the time of the blast on the chaff distribution. This study, which demonstrates the dispersion process and the resulting distribution of chaff, can provide a basis for the development and implementation of deception tactics using chaff.</p>