In a report released Monday, the congressional watchdog said that in 2008, cost overruns on the projects were 42 percent higher than initial estimates, compared with 27 percent over estimates in 2000, The Washington Post reported.
The overruns totaled nearly $300 billion, while the average delay for programs such as new fighter jets lengthened from 21 to 22 months, Gene Dodaro, acting comptroller general of the GAO, said in the report.
The GAO contended a major reason for the cost overruns is that weapons development frequently begins before the technologies used in them are mature and before designs can meet requirements for costs and schedules.
"Pentagon planners don't do a good enough job of analyzing those requirements to understand whether they have the technologies and designs to build to them," GAO analyst Michael Sullivan told the Post. "So they begin with an unrealistic baseline."
John Young, undersecretary of defense for acquisition, technology and logistics, said in the report the Pentagon in December changed its acquisition policies in an effort to carry out some of GAO's recommendations.