In most years, the Department of Defense (DoD) provides a five-year plan, called the Future Years Defense Program (FYDP), associated with the budget that it submits to Congress. Because decisions made in the near term can have consequences for the defence budget well beyond that period, the Congressional Budget Office (CBO) regularly examines the FYDP and projects budgetary impact over several decades. The CBO has produced two projections of the base-budget costs of the DoD's plans as reflected in the FYDP and other long-term planning documents released by the department. Under either projection, the costs for DoD's plans would exceed the funding that the department can receive through 2021 under the caps established by the Budget Control Act of 2011. This book presents the results of these projections, wherein the CBO has projected the costs of DoD's defence plans over the next 18 years, with a focus on gaining a more complete picture of the funding that may be needed for defence planning.