The measures indicating that a naval vessel is ready for a mission are currently perceived to include input and output performance indicators that relate to crew and vessel readiness. The psychological dynamics of crew behaviour, perceptions and compatibility levels on a particular vessel are ignored to a large extent in the determination of levels of mission readiness. This paper reviews the performance indicators used in the military in terms of readiness to achieve the desired outcome of mission readiness. It explores the importance of including the neglected area of crewing dynamics at a psychological level to determine the level of mission readiness, as well as the changing dynamics that impact strongly on the sustainability of mission readiness.