The promise of practicing mission assurance is to be able to leverage an understanding of how mission objectives and outcomes are dependent on supporting cyber resources. This makes it possible to analyze, monitor, and manage your cyber resources in a mission context. In previous work, we demonstrated how process modeling tools can simulate mission systems to allow us to dynamically compute the mission impacts of cyber events. We demonstrated the value of using this approach, but unfortunately practical deployment of our work was hampered by limitations of existing commercial off-the-shelf (COTS) tools for process modeling. To address this deficiency, we have developed our own Cyber Mission Impact Business Process Modeling tool. Although it implements only a functional subset of the business process modeling notation (BPMN), it has, unlike the more generic COTS tools, been specifically designed for the representation of cyber processes, resources, and cyber incident effects. The method and tool are described in this paper.