A common aspect of any security projection for the 21st Century is the need to function effectively in complex environments. Cluttered terrain, dense urban areas, and sub-terranean structures all present a daunting set of operational challenges for tactical units within both DoD and a host of other government agencies. The dynamic nature of urban activity and the prominence of human discord in such areas also creates a very complex and often frustrating mix of physical, emotional and psychological constraints that can prevent accomplishment of even the most simple tasks and mission sets. This paper provides an overview of DARPA’s Tactical Mobile Robotics program, and its effort to develop new technologies that will address some of the most difficult and technically challenging aspects of tactical operations in complex terrain. It stops short of an exclusive focus on urban operations in order to fully exploit the potential for semi-autonomous robotic platforms to revolutionize operations across the entire spectrum of tactical activity. This paper outlines the advantages enjoyed through the employment of Man Portable Robotic Systems (MPRS) in denied areas, and calls for a redirection of unmanned systems development toward them. A review of ground robotic platforms is provided first, followed by a discussion of operational voids and corresponding technical challenges. A very brief outline of TMR program structure is presented next in an effort to provide incremental updates on progress sought and made. The paper concludes with a call for continued support of the MRPS concept and innovative research to assist the TMR program in addressing its many technical challenges.