As the military is considering what assets it may need to conduct a potential strike on Syria, the most advanced and most expensive weapons system history will be watching from a hanger.

The F-35 Joint Strike Fighter, a do-it-all fighter for three service branches that is estimated to cost in total $395.7 billion, is simply not ready to fly into combat, despite promises from the Department of Defense early in the program.

Back in 2001 when the plane went into development, the Pentagon projected the Lockheed Martin-made fighter would reach "initial operational capability" by 2012 at the latest, according to a June 2013 report by the Government Accountability Office.

But that was before the military realized that the plane was so flawed and put into production so prematurely that the Pentagon's top weapons buyer years later would call the entire program schedule " acquisition malpractice."

Instead, by March 2007, the Department of Defense realized the plane may not be ready until 2015. Three years later in 2010, following more cost increases and production delays, it gave up on even guessing when the planes could be declared operational, according to 2012 numbers in the GAO report. The report says that the F-35 program seems to be recovering somewhat thanks to a more practical but more expensive restructuring plan, but said it "still faces considerable challenges and risks."

This May the Defense Department announced new projected "initial operational capability" dates: 2015 for the Marine Corp's version of the jet, 2016 for the Air Force's, and 2018 for the Navy's. In each case, the planes will not yet have their full range of advanced capabilities and each service will have at most two dozen planes out of the more than 2,400 that make up the full fleet.

READ: Multi-Billion Dollar F-35 Fleet Grounded | READ: Price Goes Up $771M on Most Expensive Defense Program

Winslow Wheeler, a military aviation expert and Director of the Straus Military Reform Project of the Center for Defense Information, said he believes the F-35 delays were caused by "the inherent complexity of the airplane matched up against unethically optimistic plans for both schedule and cost."

"The normal behavior by the advocates is to over-promise on cost, schedule and performance and get a commitment out of the Department of Defense and Congress before the test program starts. Then in the test program we find out what the real cost, schedule and performance is, then the advocates say, 'It's too late,'" he said. "They put together a monstrosity of complexity."

Despite the significant and costly delays, top Pentagon officials have defended the F-35 program as the most advanced weapons system ever created and the very backbone of the future of American air power. The plane, in its different variations, is designed to replace the air-to-ground fighter planes in the three services: replacing the F-16 and A-10 in the Air Force, the F-18 and F-14 for the Navy and the AV-8B Harrier for the Marines.

The F-35's fifth generation cousin, the Air Force's F-22 Raptor, went operational in 2005 and is designed to replace the air-to-air dog-fighting F-15. The F-22 has yet to be used in a military conflict and sat out during the no-fly zone operation in Libya in 2011. The Air Force said then that the plane was not an operational necessity at the time. The service did not immediately respond to inquiries about the F-22 potentially entering combat for the first time in coming days over Syria.

With regard to both planes, it's not clear what role, if any, U.S. fighters could play in an operation in Syria. Security experts have speculated the potential action would likely fall short of sending U.S. planes into Syrian airspace in favor of using long-range missiles to surgically strike targets.

Today Secretary of State John Kerry said any action would be limited in scope and would not include American "boots on the ground." He said the effort would not look like America's involvement in Iraq, Afghanistan or Libya. In the last case, U.S. fighters were deployed to assist in the no-fly zone over Libya in 2011.

READ: Syria Must Be Punished as Warning to Others, Kerry Says

Joe DellaVedova, spokesperson for the Pentagon's F-35 Program, said he imagines the services wish they could have the F-35 as an option to deploy any time thanks to its advanced capabilities, but said, "That's not the reality of where we're at."

Still, he said he was confident in the new track the F-35 is on, evidenced by recent successful night flying and weapon release testing on one variant.

"We still have more testing ahead and there are technical issues to be worked, but our data is revealing that the aircraft's capabilities and design are sound," DellaVedova said. "We're confident we'll deliver the F-35 on time to meet the warfighters' initial operating capability dates."

Representatives for Lockheed Martin did not immediately respond to requests for comment for this report.