Design of a weapon-carrier type of missile requires to provide a highly reliable mechanism of airframe separation and air stabilizer deployment which enables the safe release of payload at high-speed flight conditions. This mechanism is characterized by a relative dynamic motion of multiple separated bodies, proceeding as swiftly as hundreds of milli-seconds, so that the use of modeling & simulation(M&S)techniques could play a crucial role in the design. This paper presents an M&S technique which has been developed for a design of anti-submarine missile employing a clamshell type of airframe separation, and shows some major results of simulation compared to available flight test results. Emphasis of the current study was laid on a proper balance between the quick calculation, which is essential for practical design application, and the credibility of the results.