Over the life of the aircraft, it is expected that the USA will spend about USD1,700,000 million (1.7 true billion). To keep the aircraft serviceable, a massive stock of parts is needed from nuts and bolts, through tyres and gas canisters for ejector seats to the internal parts of the engines and weapons systems. In fact, the only things that are left out of account are the weapons and ammunition.

Some of those parts are inconsequential but many are specific to that aircraft. Many of those specific parts have little or no value in the open market, other than recyclable value - but they may have immense value on the espionage market.

But the GAO is, seemingly, not overly concerned. In fact, while being clueless as to where the items are and when they went missing, the GAO appears to think that the parts aren't missing but merely unaccounted for. And they are unaccounted for, it implies is because of paperwork errors.

"The Department of Defence owns certain F-35 spare parts that contractors manage. But the department doesn't account for or oversee the parts. This is in part because various Department offices and contractors haven't agreed on whether the spare parts should be categorised as government-furnished property."

This, the GAO, says is the root cause and "of about a million lost parts worth USD85 million, the Department of Defense only reviewed the circumstances surrounding 2% of identified losses since 2018."

The GAO expands its reasoning but the explanation only seems to make matters worse: "One contributing factor to the Department's lack of accountability over these spare parts is the lack of agreement among various organisations as to whether the spare parts are both accountable under a contract and government-furnished property. If the spare parts, which include engines; tyres; landing gear; and other parts, such as bolts, screws and fasteners, are not accountable under a contract and are not government-furnished property, the contractor will not enter these parts into the system the Department uses to track losses and disposition. Without the Department taking steps to ensure that these spare parts are accountable under a contract, the F-35 Joint Program Office will be unable to either gain or maintain accountability over these spare parts and will not have data, such as locations, costs, and quantities, needed for financial reporting or to ensure that government interests are protected."

So, to summarise: the Department hands over parts and equipment to external contractors, or has them delivered direct, and they fall through the cracks of an internal audit system because no one says "those are ours, look after them and make sure you copy us in on your stock records."

And this is only the tip of a very messy iceberg.

Further Reading: https://www.gao.gov/products/gao-23-106098