The U.S. Department of Defense (Pentagon) prevented the publication of an annual report mandated by Congress on the controversial and extremely costly F-35 fighter jet program for the first time in more than two decades, according to Bloomberg.

An official at the U.S. Government Accountability Office (GAO), an independent nonpartisan oversight body, said Pentagon officials concluded that the annual assessment of the fighter program, whose total cost is estimated at about $1.6 trillion, includes 'controlled unclassified information,' which prevented the publication of any part of the report to the public.

The report was a key window into the details of the most expensive and advanced defense program in the world. But this time, only the title of the assessment, issued on June 25, was published: 'F-35 Joint Strike Fighter: Perspectives on Production and Modernization Efforts.'

John Ludvigson, director of the GAO's Acquisition and Sourcing Management team, who oversaw the report's preparation, said the office 'has been monitoring the F-35 acquisition program annually since Congress mandated these reviews starting in 2005.'

He added that this is the first time any of the office's reports on weapons programs have been classified as containing controlled information, preventing its public release.

He explained that the report, despite being withheld from the public, was delivered to members of the four defense committees in Congress, and the office continued its mission of informing the relevant committees of progress in the fighter program's modernization efforts.

Repeated criticism of the program and the mechanism for withholding information. The F-35, produced by Lockheed Martin, is the most expensive weapons system in U.S. history, but it has repeatedly faced criticism for cost overruns, delays in engine and aircraft deliveries, troubled software updates, and components wearing out faster than expected.

Last year's GAO report concluded that the F-35 program 'continues to overpromise and underdeliver.'

Spokespersons for the Department of Defense and the F-35 Program Office did not respond to Bloomberg's requests for comment.

Pentagon spokesman Sean Parnell said that Defense Secretary Pete Hegseth is running 'the most transparent Department of Defense in history.'

The annual GAO report is the most detailed public source for evaluating the performance of one of the most closely watched weapons programs inside the Pentagon, as previous editions revealed significant delays in software, equipment, and engine updates.

These reports also serve as an important reference for lawmakers in countries that have purchased the fighter, including the United Kingdom, Israel, Japan, and Poland.

The classification of 'Controlled Unclassified Information' (CUI) has faced repeated criticism from U.S. lawmakers who say its broad definitions give the Pentagon wide authority to withhold information it does not want to release, even if it is not classified as secret.

The Pentagon has also previously withheld GAO reports on efforts to modernize the nuclear arsenal during the administration of former President Joe Biden.

In one case in 2023, the Defense Department restricted the publication of a report that criticized the reliability of the timeline for building Columbia-class nuclear-armed submarines.