“The Department of Defense’s (DoD’s) budget consists of appropriations for the following purposes: compensating military personnel; developing and purchasing weapons; building bases, facilities, and housing; and supporting day-to-day operations. The largest single appropriation category in DoD’s base budget is the operation and maintenance (O&M) account, which funds day-to-day operations ranging from health care to equipment maintenance. Over the past few decades, funding for O&M has increased substantially, accounting for a growing share of DoD’s budget. That growth has occurred even as the number of active-duty military personnel has remained flat or declined. Consequently, Members of Congress and the defense community at large have expressed concerns about this portion of DoD’s budget. However, efforts to identify the activities that have contributed significantly to the growth in spending are complicated by the diverse nature of the goods and services purchased with O&M funds and limitations associated with available data. Nevertheless, CBO’s analysis indicates that increased funding for large and familiar categories, such as the military health care system, civilian pay, and fuel, accounts for about 60 percent of the long-term growth in O&M funding; varied smaller and lesser-known activities, such as contracted services and the operations of small DoD agencies, account for the remaining 40 percent. Of those varied and lesser-known activities, funding increased significantly for the maintenance of equipment, weapon systems, and property; technical and research services; professional and other services; and purchases of equipment not part of weapon systems.”