The Government Accountability Office previously stated in March 2021, "The F-35 programme is more than three years into Block 4 development, but it has not produced new capabilities as promised." The GOA projected the cost of the upgrading at $14 billion.

According to the 13-page assessment in the testing office's annual report, which will be released soon, aircraft operators "identified deficiencies in weapons, fusion, communications and navigation, cybersecurity and targeting processes that required software modification and additional time and resources, which caused delays."

The F-35 is mostly described as a flying computer with more than 8 million lines of computer code, and issues have plagued the software required to expand its capabilities since delivery of the upgrades began in 2020.

According to the report, the Defence Department's F-35 programme office has adopted " process improvements to address software development issues."

The F-35 component of the annual report, circulated for discussion inside the Pentagon, is a mix of unclassified and " controlled, unclassified information."

The Block 4 software upgrade includes a new processor that boosts the F-35's computing power and memory. The Block 4 software has a new to increase the. The upgrade also is intended to allow the fighters to carry new AIM-9X Block II air-to-air missiles, all-weather Small Diameter Bomb II munitions, radar-killing AARGM-ER missiles, several allied-produced bombs and the B-61 nuclear bomb.