The Department of Defense (DOD) is embarking on a number of efforts to enhance warfighting and the way the department conducts business. Major investments are being made to develop improved weapon systems to combat various threats to U.S. security. While the weapons that DOD ultimately develops have no rival in superiority, weapon systems acquisition remains a long-standing high-risk area. GAO's reviews over the past 30 years have found consistent problems with weapon acquisitions such as cost increases, schedule delays, and performance shortfalls. In addition, DOD faces several budgetary challenges that underscore the need to deliver its new major weapon programs within estimated costs and to obtain the most from those investments. DOD can help resolve these problems by using a more knowledge-based approach for developing new weapons. This report provides congressional and DOD decision makers with an independent, knowledge-based assessment of selected defense programs that identifies potential risks and needed actions when a program's projected attainment of knowledge diverges from the best practice. It can also highlight those programs that employ practices worthy of emulation by other programs. GAO plans to update and issue this report annually.