We conducted simulations to analyze the effects of a hard-kill-type underwater defense system that defends friendly warships against an enemy wake-homing torpedo. Assuming that the enemy torpedo is a wake-homing torpedo, our surface warship detours to the prespecified evasive course by firing a hard-kill-type system, which is modeled as a passive acoustic homing-torpedo, to attack the enemy torpedo. We analyzed the effectiveness of a warship’s survival probability via Monte Carlo simulation, given the probabilistic angles of the launched torpedoes, to compare two cases where one used only evasive maneuvering and the other used the hard-kill-type underwater defense system with evasion at the same time. By changing the maximum torpedo detection range of a warship and the torpedo’s initial location, we observed that the resulting survival probability of a warship was above 61% with a hard-kill-type defense system, whereas it remained at 34% without a hard-kill defense system, the necessity of a hard-kill underwater defense system, especially against wake-homing torpedoes.