In 1997, Lockheed Martin earned the distinction of being one of two final competitors for the Pentagon’s revolutionary new Joint Strike Fighter concept program. Within four years, they had beaten out the competition at Boeing and secured victory for their X-35 concept. Five years after that, in February of 2006, the first production F-35A rolled off the assembly line and ten months later, an F-35 took to the skies for the first time. Flights of production aircraft began in 2011 and deliveries of the fighter began later in that same year.

By 2015, the Marines declared their iteration of the F-35 (F-35B) had reached initial operating capability, with the Air Force following a year later and the Navy joining the party earlier this year. All told, more than 380 of the advanced fighters have been built and shipped to bases around the world thus far… but according to the Pentagon, the most expensive aircraft ever developed in history still doesn’t appear to be ready to enter into full production.

“I’m going to make some decisions about when that full-rate production decision will be made shortly,” Under Secretary of Defense for Acquisition and Sustainment Ellen Lord said on Friday, following the revelation that a number of Pentagon officials are not planning on signing off on the F-35 entering into full-rate production until as late as January of 2021, marking yet another delay in a program that has been plagued with high profile issues and setbacks.

The Initial Operational Test and Evaluation (IOT&E) period for the F-35 was expected to finally come to a close earlier this summer, but the testing end date was pushed back due to an issue with the program’s Joint Simulation Environment.

“We are not making as quick progress on the Joint Simulation Environment integrating the F-35 into it. It is a critical portion of IOT&E,” Lord said to reporters, adding that inspectors need to get the Joint Simulation Environment “absolutely correct” before further testing can be done. That Joint Simulation Environment, or JSE, simulates mission scenarios such as different kinds of weather, geography, and distances — allowing pilots to test the aircraft’s “full capabilities against the full range of required threats and scenarios.”

Now it appears this important element of testing, which was originally scheduled for September of 2018, may not be complete for more than another year, pushing back full scale production of the F-35 for just as long, despite the U.S. military and a number of partner nations already using these aircraft in combat.

The F-35 has faced repeated setbacks due to issues with the platform identified throughout the past two-plus decades of testing. In fact, one can attest that much of the program’s cost overruns can be attributed to the Pentagon’s decision to begin production and deliveries of these fighters long before testing was complete, resulting in a number of aircraft needing costly overhauls to address issues that weren’t identified until after the deliveries had been made.