In its planning, the Department of Defense needs to assure development of a number of important campaign-level building-block capabilities, one of which is the capability--even with short warning and complications such as reduced access or air defenses--to stop an invading army quickly and as far forward as possible to avoid significant losses of territory and damage to the defending nation, and to reduce the military and political difficulty of subsequent counteroffensives. There are many possible ways to achieve such a capability. This study describes a prototype high-level "exploratory analysis" of the halt-phase problem, one that considers a very wide range of operational circumstances and a diversity of forces with an emphasis on precision fires from aircraft, ground-force missiles, and naval missiles. The work described was accomplished with a simple spread-sheet model, an experimental design involving many tens of thousands of cases to survey a "scenario space," and RAND's Data View system for examining results of an exploratory analysis.