It is difficult to apply the ram target value setting methods of the conventional weapon system to a large combined weapon system such as a submarine. The current study presents the case of weapon system development and suggests a new way to improve the setting and verification methods of ram target value of the submarine through critical review of the case. The submarine, unlike other weapon system, has an operating environment, which reaches all over the world, and its operating and maintenance conditions are different from others. Therefore, the ram target value of the submarine should be set and verified on the basis of mission essential equipment and mission critical equipment, not of all the constituent components.