The U.S. Department of Defense (DOD) workforce is made up of approximately 3.7 million people. One-third (1.3 million) are Active Duty, while the remaining two-thirds are divided among the Selected Reserve, DOD civilian employees, and contracted services/support full-time equivalents (FTEs). To shape a larger, more capable, and more lethal joint force, the Secretary of Defense requested a comprehensive review of personnel force structure and utilization polices. This includes evaluating the potential for permanently separating non-deployable Service members, assessing the warfighting relevance of professional military education and mandatory training requirements, and examining hiring practices for the civilian workforce. These topics are complex and far reaching. Can novel workforce structures be used to extend the reach and lethality of DOD resources by using different combinations of the workforce? How might DOD implement its Workforce Rationalization Plan and optimize investments across the dimensions of military personnel, civilian employees, and contractor support; active duty, reserve, and National Guard personnel; officer, warrant officer, and enlisted personnel; and human performers versus technology substitution? We consider changes to workforce mix practices, policies, regulations, and statutes that may produce greater readiness and lethality across the departments human capital portfolio. Focusing on the expeditionary, training, and medical workforces, we summarize what is currently known about which labor types are best suited for a given objective, illuminate knowledge gaps, highlight currently actionable research insights, and outline strategic research questions to pursue now in advance of tomorrows information demands.