Delays in testing critical software for the F-35 Joint Strike Fighter could derail the stealth aircraft’s scheduled 2015 debut for regular combat-ready duty with the U.S. military, according to a watchdog report released this week.

Congress’s nonpartisan Government Accountability Office said the setbacks “may hinder delivery of the warfighting capabilities the military services expect.”

The Marine Corps expects have combat-ready F-35s by July 2015, but the GAO determined that the military may need to postpone that date by up to 13 months because of the testing issues. “The effects of these delays compound as they also put the timely delivery of Air Force and Navy initial-operating capabilities at risk,” the report said.

The Air Force and Navy are scheduled to have combat-ready F-35s by 2016 and 2018, respectively. The aircraft will have different capabilities for each branch of the service that uses them.

The U.S. Marine Corps version of the F-35 Joint Strike Fighter. (REUTERS/Lockheed Martin.)

In its response to the findings, the Defense Department agreed to report to Congress on the risks associated with sticking to the existing timetable for delivery of the Joint Strike Fighters.

Air Force Lt. Gen. Chris Bogdan, who heads the F-35 program, said in a statement that he is confident the F-35 will have its required warfighting capabilities on time for the Marine Corps, Air Force and Navy.

“There were no surprises in this report and all of the items mentioned were well-known to us, the F-35 international partners and our industry team,” Bogdan said in a statement. “Software continues to remain our number one technical risk on the program and we have instituted disciplined systems engineering processes to address the complexity of writing, testing and integrating software.”

Lockheed Martin, the manufacturer of the aircraft, said in a statement that it expects to have the required combat-ready software ready for the Marine Corps by July 2015.”Lockheed Martin remains confident we will complete flight testing of the software required for Marine Corps Initial Operational Capability this year,” said company spokesman Michael Rein.

GAO described the F-35 program as the Pentagon’s “most costly and ambitious acquisition program” ever. The U.S. government is projected to spend $400 billion to develop and purchase the multi-role fighters, in addition to hundreds of billions more to operate and maintain them, the agency said.

The F-35 program has a history of budget, performance and deadline problems. The cost and schedule estimates have largely stabilized after a 2012 overhaul of the program, but the persistent software problems could throw everything off again, the report said.

The GAO determined that cost-cutting may be necessary to keep the program within its budget. “DOD has already made a number of difficult decisions to put the F-35 on a more sound footing,” the report said. “More such decisions may lie ahead.”

Full-scale production of the Joint Strike Fighters is scheduled to begin in 2019, with Lockheed Martin supplying more than 2,400 of the aircraft to the U.S. military by 2037.

The GAO said the F-35 program would cost $1 trillion to operate and support over its lifetime, but defense officials have determined that price to be unaffordable given recent budget constraints, according to the report.

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