Introduction: The conflicts in Iraq and Afghanistan were characterized by air superiority for US forces, asymmetric engagements, and irregular combat operations. Large-Scale Combat Operations (LSCO) that are anticipated in the future will differ in both scale and tactics – including contested air superiority, and conventional combat operations against peer and near- peer adversaries. This literature review aims to provide a comprehensive overview of the evolution and performance of Role II and III units, in order to inform innovations in support of LSCO. Materials and Methods: We performed a scoping review of the available literature on Role II and Role III facilities in the US Military Health System from 1900-Present. In total, 51 articles and books/chapters were identified. These were abstracted by two study authors, with any discrepancies adjudicated by a senior author. Compiled data included the types of Role II and III units (or military medical units that performed in similar fashion) in the time period 1900- present, their assigned personnel, and performance in combat operations. Results: The current composition and use of Role II and III facilities primarily reflect the nature of combat experience in Iraq and Afghanistan. The lack of air superiority, increased reliance on ground transportation and the volume of high-acuity combat casualties are anticipated to be major challenges to Role II and III facilities in the context of future LSCO. The “Golden Hour” principle that was successfully implemented during the Iraq and Afghanistan conflicts will be difficult to adhere to without adjusting the composition and capabilities of Role II and III units. Increased flexibility, interoperability and mobility, with a reliance on larger cadres of surgical and intensive care specialists with greater familiarity with military techniques and operational medicine are anticipated to be necessary. Conclusions: Given the characteristics of LSCO, we anticipate less of a “one-size fits all” capability for military medical units in the future and the need for robust medical units as close to the front lines as possible with an emphasis on prolonged casualty care and emerging technologies for patient movement and logistical supply.