Abstract: Accurate modelling and simulation of ship motions in seaway is essential due to these results would be used to improve ship functions in aspect of safety and reliability in service, regularity and adequate operation. This study presents an overview of mathematical models in Marine Systems Simulator (MSS) which is a MATLAB/Simulink library and simulator for marine systems. This models simulate real-time six degree of freedom ship motions (pitch, heave, roll, surge, sway and yaw). The well-known US Navy combatant, DTMB 5415 test cases are used to verify and validate the accuracy of case studies.