Combat Service Support Elements (CSSEs) for the U.S. Marine Corps deploy with a limited number of spare parts to keep the fighting unit at its highest level of readiness. Items that are requested by the unit, but not carried by the CSSE, are backordered, resulting in lower readiness and additional transportation costs. We show how to determine which items the CSSE should take, and in what quantities, to best support a fighting unit. We have tested our model on data from a recently deployed Marine Expeditionary Unit (MEU), and the results suggest that the MEU could have experienced 13 percent fewer backorders and saved $11,007 in shipping costs by using the model.