All navies, when taking initiative to build a new platform, have difficulties with determining in an early phase the number of people that are needed to sail the planned ship. How do you approach this problem? How can you reduce the complexity of it? How do you reach a cost-effective solution? How do you coordinate all the stakeholders and experts involved in this process? At TNO, we have reflected on a dozen of human centred design projects for the Dutch Defence Materiel Organization (DMO). We have unified many years of developed knowledge, methodologies and tools in one Manning Centred Design framework, aimed at reducing the complexity of such design problems, managing the risks involved, and capturing the applied knowledge and experiences for later use. In this paper, the framework will be explained and illustrated by two projects: the development of the Offshore Patrol Vessel and the Submarine Life Extension Program.