This report is GAO's fifth annual assessment of selected weapon programs. From 2001 to the present, the Department of Defense (DOD) has doubled its planned investment in new systems from approximately $750 billion to almost $1.5 trillion. While DOD expects these systems to transform military operations, their acquisition remains a high-risk area. GAO's reviews of weapons over three decades have found consistent cost increases, schedule delays, and performance shortfalls. The nation's growing long-range fiscal challenges may ultimately spur Congress to pressure DOD to cut spending on new weapons and to redirect funding to other priorities. In response, DOD might be compelled to deliver new weapon programs within estimated costs and to obtain the most from its investments. This report provides congressional and DOD decision makers with an independent, knowledge-based assessment of selected defense programs, identifying potential risks and needed actions when a program's projected attainment of knowledge diverges from the best practices. Programs assessed were selected using several factors: high dollar value, acquisition stage, and congressional interest. This report also highlights issues raised by the cumulative experiences of individual programs. GAO updates this report annually under the Comptroller General's authority to conduct evaluations on his own initiative.