Small unit performance is an area of human systems integration that is often neglected, but includes requirements and constraints that are different from the concerns for individual human performance. The unique considerations associated with small unit performance extend to such topics as team building, maintaining team cohesion, team performance (e.g., collaboration, communication, coordination of tasks, situation awareness, and decision-making) and metrics, team training (e.g., applications of immersive training environments), team resilience and grit in extreme environments. The Department of Homeland Security (DHS) is collaborating with the US Joint Forces Command (USJFCOM) National Program for Small Unit Excellence to develop requirements, concepts, methods and metrics for enhancing the performance of incident First Responders, including police, firefighters, emergency medical technicians, and personnel involved in detecting and responding to the hazardous release of chemical, biological, and radioactive materials. Many products will result from this collaboration including techniques to enhance the communications, coordination and collaboration among First Responders, instruction delivery methods to ensure effective training for team performance, design requirements for protective equipment and clothing, wearable electronics to facilitate incident management, alarms and alerts, and outreach to public health organizations. The analytic method proposed to address these issues and produce these products is the Top Down Requirements Analysis (TDRA) process that is being developed and implemented by the DHS. This process begins with generation of scenarios that pose significant challenges to human performance, workload, health and safety, proceeds through function analysis and allocation of functions to task analysis, to establish the requirements associated with task performance under the conditions specified in the scenarios.