Lockheed Martin has marketed the F-35 successfully to 14 countries over nearly 20 years. Subtracting Turkey’s canceled program for 100 jets, Lockheed still boasts commitments from 13 countries to buy nearly 3,220 F-35s, with deliveries projected out to 2046. Three more countries with a combined requirement for about 200 fighters are evaluating the F-35 in competitive tenders, and another five have publicly discussed a long-term interest in acquiring the aircraft.

• U.S. Air Force and Marine Corps send conflicting signals

• UAS and F-15EX increase F-35 competition

That is the good news for the only supersonic, stealthy fighter with a short-takeoff-and-vertical-landing variant on the export market today.

But that otherwise optimistic sales outlook is clouded by resource constraints, shifting priorities and new technological advances that threaten a large portion of the planned orders in the F-35 program of record. Moreover, the recent expulsion of Turkey from the program because of its acquisition of Russian military hardware highlights rising pressure from political interference on high-profile foreign arms sales.

The U.S.-led F-35 Joint Program Office declared in 2009 that total sales of the F-35 could reach 6,000, but more than a decade later government and Lockheed officials prefer to size the global market at around 4,000. Even the more modest projection may depend on maintaining the original orderbook of the U.S. Air Force, the program’s largest customer, with an official requirement for 1,763 F-35As.

Although Air Force leadership remains fully committed, cracks have appeared in the service’s long-term programming. In March, Air Combat Command (ACC) announced a goal to achieve a long-term fighter fleet composed of 60% F-35s and Lockheed F-22s and 40% among Boeing F-15s, Lockheed F-16s and Fairchild Republic A-10s. The Air Force inventory today counts about 2,190 fighters overall, leaving room for a total of about 1,315 F-22s and F-35s combined to achieve the 60% goal. If about 180 F-22s are removed from the equation, the Air Force would be left with a total fleet requirement for 1,135 F-35As.

The Marine Corps, which plans to buy 357 F-35Bs, faces similar pressures. In March, the Marine Corps announced plans to cap F-35B squadrons at 10 aircraft each, eliminating plans to field nine of 14 F-35B squadrons with 16 aircraft. The decision appears to create an inventory surplus of about 54 jets, but the Marines have not made any changes to the program of record.

Similar constraints are visible in other countries. The UK is in the midst of a defense review with officials scrutinizing plans for the Royal Air Force and Royal Navy to acquire a total of 138 F-35Bs, of which only the first 48 are funded so far. Alongside plans to upgrade the Eurofighter Typhoon and develop the Tempest next-generation fighter, the Defense Ministry will have to balance resources carefully.

The military technology advances add further pressure. The U.S. Air Force is developing a new class of low-cost attritable unmanned aircraft systems (UAS), which the service envisions performing as reusable munitions to augment the sensor and weapons capabilities of aircraft such as the F-35. As the technology matures, ACC sees the potential for using swarms of attritable UAS to replace hundreds of the Air Force’s oldest F-16s, which are due to enter retirement in the second half of the decade.

But demand for the F-35 still is growing in other areas. The U.S. government’s recent approval of 105 F-35s for Japan shows how the international program still can expand. Japan originally acquired 42 F-35s in 2014 to replace an aging fleet of McDonnell Douglas F-4s. The newly approved acquisition would expand the F-35 fleet to replace Japan’s oldest F-15s. Israel, meanwhile, already has ordered 50 F-35s. As a political leadership crisis moves toward stability, Israel soon could sign a follow-on order for up to 75 new jets, with the F-35A and F-15EX splitting the deal.

Other countries still are seeking to enter the program. Singapore has been approved by the U.S. to order up to 12 F-35Bs. In January, the prime minister of Greece announced plans to order F-35As after a batch of upgraded F-16s are delivered in 2024. The U.S. government also has named Romania and Spain in Europe as potential F-35 buyers. In the Middle East, the United Arab Emirates and Saudi Arabia are busy absorbing new Dassault Rafale and F-15SA jets, respectively, but are likely to consider the F-35 in the second half of the decade.