What is the best approach to define a Modelling and Simulation as a Service (MSaaS) operational capability in a military domain such as the NATO and Allied Community of Interest? This paper is intended to illustrate how the existing state-of-the-art technology can be incorporated into MSaaS concept to support M&S applications in the military domain. NATO MSaaS is a means of delivering value to customer nations via Internet cloud technology by enabling access to M&S applications, capabilities, and data without nations incurring the costs associated with ownership. The MSaaS concept is under development by NATO Modelling & Simulation Group (NMSG), with contributions from NMSG 131 and its successor NMSG 136. In accordance with NATO Concept Development & Experimentation for Modelling and Simulation, the authors propose the application of the NATO Comprehensive Approach (CA) to define the Allied Framework for MSaaS operational concept, considering all DOTMLPFI domains (Doctrine, Organization, Training, Material, Leadership, Personnel, Facilities, Interoperability). The M&S CoE has been applying the NATO CD&E process and NATO Comprehensive Approach to develop a sub-concept to analyze and support the evolution of a real use-case, “MSaaS supporting the NATO Urbanization Projectâ€�. In conclusion, the research has emphasized how Modelling and Simulation as a Service can be adopted to support operational capability development, related reference architectures (RA), and business models for NATO.