The Defense Department has launched 20 or more projects to build modern business-management systems since the late 1990s. At least five were subsequently killed as complete failures after billions of dollars were spent on them. With each failure, a pattern emerges: An off-the-shelf product with a proven track record in the private sector is chosen and then modified to the point where it doesn't work properly. The Pentagon is unable to account for itself, and thus for roughly half of all congressionally approved annual federal spending. Interviews with scores of current and former defense officials, contractors and Pentagon watchers, as well as a review of dozens of reports by oversight agencies, show that the Pentagon is continually thwarted by a lack of accountability for failures ... and an incentive to spend. All other federal agencies are audited annually ... and with rare exceptions, they pass every year. The Pentagon alone has never been audited, leaving roughly $8.5 trillion in taxpayer dollars unaccounted for since 1996. The Pentagon has for years kept lousy books with impunity. The 2009 law requiring the Defense Department to be audit-ready by 2017 provides for no penalties if it misses the deadline. From 1995 through 2002, Senator Charles Grassley pushed through an amendment to the annual defense appropriations bill requiring the Pentagon to account for its expenditures by following one seemingly simple procedure: match each payment to the expense it covered. The order was ignored, and Grassley gave up. There is no doubt that bad bookkeeping conceals movements of money that in some instances are illegal.