Absent significant changes in U.S. defense investment priorities, American forces could soon find themselves unable to cope with some emerging challenges in large-scale power projection operations. Specifically, U.S. forces will need better capabilities to secure a foothold in distant theaters, to defeat weapons of mass destruction and their delivery vehicles, to gain control of operations in the air, and to locate and destroy invading ground forces. New surveillance sensors, information processing capabilities, communication systems, and guided munitions are enabling operational concepts that can allow U.S. forces to meet emerging challenges and, indeed, to adopt new approaches to warfare. The authors assess quantitatively the capabilities of U.S. forces in the context of a generic scenario depicting a large-scale war in the next decade. From this, they identify priorities for modernizing U.S. forces. They argue that modernization dollars should be focused on forces and enabling capabilities that allow for decisive operations early in a conflict. If necessary, funds for such enhancements can come from modest reductions in forces that are slower to deploy.