The convergence of various industries and complexity of weapon system development environments require the application of a systems engineering-based development methodology to secure high-quality weapon systems. Capability maturity model integration (CMMI) is a model for evaluating the maturity of an organization's development capabilities, and is widely used as an industry standard for evaluating systems engineering-based process capabilities. In situations where weapon system acquisition types are diversifying from conventional methods such as system development to rapid research and development, and industry boundaries are disappearing, organizations must internalize systems engineering-based development and development management processes. This study presents a case study of internalization in an organization with high process maturity. Based on the maturity level of the organization, the following strategies and methods are suggested for internalizing CMMI-based processes. For CMMI-based process internalization, we present the methods and effects of strengthening process implementation capabilities in low-maturity organizations, as well as examples of improving measurement systems and developing and applying process performance management tools for quantitative assignments in high-maturity organizations. This enables us to successfully achieve and maintain the CMMI-DEV Level 5 certification six consecutive times.