The U.S. Government Accountability Office and the Pentagon Inspector General have raised issues with the F135 engine program.

By Georges Seguin (Okki) (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons

The GAO has deemed that the “reliability of the engine is very poor” and that “the program has a long way to go to achieve” reliability goals.
To make matters worse for Pratt & Whitney, the Pentagon’s internal watchdog found 61 violations of quality management rules and policies during an inspection.
Pratt & Whitney defended the program by saying that the GAO had failed to take into account new designs that have been validated and are being incorporated into the engine.

Source: Alert 5