Abstract: Objectives This study systematically investigates the influence mechanisms of external waves on the motions of damaged ships, aiming to reveal the dynamic response characteristics of damaged ships in waves and provide theoretical support for improving their survivability at sea and mitigating marine environmental risks. Methods Based on a self-developed viscous flow RANS (Reynolds-Averaged Navier-Stokes) solver, a full-time-domain direct numerical simulation was conducted to study the motion responses of a starboard-damaged DTMB (US David Taylor Model Basin) 5415 ship in regular waves. The numerical model fully considers key physical processes including fluid viscosity effects, tank sloshing, and internal-external fluid exchange at the opening of the damaged compartments. First, the model accuracy and reliability were validated through wave generation verification, mesh and time-step convergence analysis, and comparison with experimental data. On this basis, a systematic analysis was carried out on the motion responses of the damaged ship in regular waves from different wave directions, with a focus on the influence of wave direction on ship motion characteristics. Results The results indicate that wave direction significantly affects roll amplitude, while its effect on pitch and heave amplitudes is relatively small. For a midship-damaged vessel, higher roll amplitudes and stronger asymmetry were observed under port-bow/port-quarter waves compared to starboard-bow/starboard-quarter waves. Conclusions The study reveals the mechanisms by which wave direction influences the motion characteristics of damaged ships, providing valuable insights for enhancing the safe navigation performance of damaged ships in complex wave environments.