During 20042005, three consecutive category-5 storms hit the central region of Gulf of Mexico (GOM) and damaged numerous drilling and production platforms. Since then, a number of forensic studies have been conducted to better understand the failure causes and mechanism. In this study, a representative deepwater semi-submersible Mobile Offshore Drilling Unit (MODU) that suffered a mooring failure and went adrift during the hurricane Ivan was selected for numerical forensic study. The platform responses and progressive mooring-line failure are simulated in the time domain. A time-domain vessel-mooring coupled dynamic analysis computer program is used to simulate the sequence of progressive mooring-line failure of the MODU in the hindcast Ivan environment, in which the wind, wave, and currents were non-collinear. The case of non-collinear environment is also compared with that of collinear environment. The numerical prediction and simulated results are compared with the available field-analysis data.