Buying more of a good fighter sounds like an easy win. The Pentagon has just published the fine print, and it is a reminder that in defence procurement, doubling an order is never simply a matter of writing a bigger cheque.

Earlier this year the U.S. Air Force announced it would grow its planned F-15EX Eagle II fleet from 129 aircraft to 267, more than doubling the buy in order to replace the ageing F-15E Strike Eagle. The August selected acquisition report for the programme, reported on 2 September, sets out what that decision actually costs in risk.

The short version: more lots, older suppliers, a production line that is already late, and a bill nobody has finished adding up.

Four more lots, and a technical refresh nobody has priced

The previous acquisition strategy ran to eight production lots. The new one runs to twelve. That stretches the F-15EX line years further into the future, and the report is blunt about what that means: Boeing will likely have to conduct “a major technical refresh” to cope with diminishing manufacturing sources and material shortages.

Put plainly, the parts that go into an Eagle II today will not all still be in production when the last one is built. The radar, the mission computer, the electronic warfare suite and the engines could all become obsolete inside the programme’s new lifespan. Replacing them mid-run is, in the report’s own words, “a significant redesign effort.”

The programme’s answer is to fold those upgraded subsystems into scheduled operational flight program releases between 2031 and 2035, so that testing and fielding happen without stopping the line. It is a sensible plan. It is also a plan that assumes eight more years of stable funding, stable suppliers and stable requirements.

The bill has not been added up yet

Here is the line that ought to make a budget analyst sit up. Programme officials say they have not yet fully estimated what extending production will cost. They have started a rapid cost estimation process to feed the fiscal 2028 request, and in the meantime are using government estimates for initial budget sizing while “commissioning formal studies to obtain preliminary cost and schedule estimates from the contractors.”

The Air Force has committed to 138 additional fighters and is now working out what they cost. That is not unusual in American defence procurement. It is not reassuring either.

Boeing declined to comment on the concerns raised in the report.

A strike that will not be recovered from

The near-term problem is more concrete. From August to November 2025, a strike shut down Boeing’s St. Louis plant. The report says the resulting slip is permanent: Boeing’s contract required all 12 Lot 3 jets to be delivered in early calendar 2026, and only six will arrive by the end of the year. The report calls these “unrecoverable delays.”

Parts shortages compound it. The most acute are the Elbit-built large area displays and low-profile head-up displays that give the Eagle II its glass cockpit, General Electric F110 engines, and Collins-made cartridges for the ejection system. Stockpiling during the strike covered Lot 1B. Later lots are exposed, and the Pentagon has resorted to borrowing-and-payback arrangements with foreign military sales customers to keep critical parts flowing.

Boeing on the F-15EX production line in St. Louis, the plant that now has to double its output rate.

Kadena keeps waiting

The delays land hardest in Okinawa. Kadena Air Base lost its permanently assigned F-15C and D Eagles when the Air Force began retiring them in November 2022, and has been covered by a rotating cast of visiting fighter squadrons ever since. The F-15EXs meant to end that arrangement were supposed to start arriving in spring 2026. They are now not expected before the first quarter of fiscal 2027 at the earliest.

Lot 4 is worse: deliveries that should have begun in 2026 are now forecast for calendar 2028. To catch up at all, Boeing has to hit two aircraft a month.

The programme office is working with Air Combat Command and the National Guard Bureau on a bridging strategy — keeping older jets or alternative force structures available until the Eagle IIs actually turn up. Which is the real story buried in this report. The Air Force is not short of a plan for the F-15EX. It is short of F-15EXs.

Sources: Air & Space Forces Magazine, U.S. Department of Defense F-15EX Selected Acquisition Report (FY2027 President’s Budget), U.S. Air Force / DVIDS.