Since their first induction the United States Air Force and Marine Corps the F-35 Lightning II light stealth fighters' performance issues and unreliability have been notorious - far eclipsing the problems faced by its predecessors the F-16 and F-5. Critical maintenance issues stemming from the platform's complexity, as well as severe problems with software, have seriously affected the fifth generation fighter's availability for combat missions. Design flaws include crumbling fuel tanks, inability to refuel in the air and technical difficulties related the launch AIM-120 anti aircraft missiles and the release of air to ground munitions. Several clients for the fighter including Canada, Israel and Denmark have expressed much skepticism regarding the platform's ability to meet expectations. According to Robert Behler, the Defense Department’s new director of operational testing, the availability of the fighter for missions remains “around 50 percent, a condition that has existed with no significant improvement since October 2014, despite the increasing number of aircraft.” This was noted in an annual report delivered to senior Pentagon leaders and congressional committees on January 23rd.
While the F-35 fighters are produced in large numbers, efforts to improve their reliability have been "stagnant." It is hardly uncommon for aircraft to remain out of service for extended period awaiting spare parts. The fighter are by far the most high maintenance light platforms in the world, with all other fighters of their kind being designed to prioritize low maintenance and reliability much as the F-16 did. Extreme maintenance needs mean the F-35 can fly less than once a week even with all the parts required available. This combined with its high acquisition and operational costs have made it highly unsuitable for service as a light multirole platform to replace the F-16. Several Pentagon officials including chief weapons buyer Ellen Lord and Deputy Defense Secretary Patrick Shanahan noted the $406.5 billion projected acquisition cost for the program and $1.2 trillion total cost for the program - leaving each fighter costing several times as much as the F-16 they replaced while being able to fly less often and carrying less munitions. The Defense Department is nevertheless moving to accelerate contracting and production. How this will impact the combat readiness of the United States military, and whether the approximately 2,000 units on order will all be completed and delivered, as of yet remains to be seen.