A $US14 billion ($19.5 billion) Pentagon software upgrade for F-35 jets is being installed on planes that are already deployed even though it’s “immature, deficient and insufficiently tested”, according to a new assessment by the military’s testing office.

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”, according to the 13-page assessment in the testing office’s annual report, which will soon be released.

Bloomberg