Tokyo will review indigenous production of the Lockheed Martin F-35 fighter with an eye to saving production costs.

No decision has been made about the fate of long-term F-35 production in Japan, but the Japanese government clearly sees potential to save costs by taking jets from the main Fort Worth production line, according to a government document viewed by FlightGlobal.

Tokyo is replacing its McDonnell Douglas F-4 Phantoms with the F-35, and ordered 42 examples in 2011. Of these, four were built at the Fort Worth production line, with the remaining 38 to come from a final assembly and checkout (FACO) line set up by Mitsubishi Heavy Industries in Nagoya.

In December, Tokyo announced plans to order 105 additional examples.

A source familiar with the production review says that the original 38 aircraft production run will go ahead as planned, but that it is not a given that some, or any, of the extra F-35s that Tokyo plans to obtain will be produced indigenously.

The Nagoya line rolled out its first F-35A in June 2017 – the fifth F-35A delivered to the Japan Air Self Defense Force. Flight Fleets Analyzer shows that Tokyo’s in-service F-35A fleet has grown to 10 examples, suggesting a production rate of under three aircraft annually.

At the Farnborough air show in July 2018 Greg Ulmer, vice president and general manager of Lockheed Martin’s F-35 programme, said that the Japanese FACO will ramp up to a maximum capacity of six aircraft annually in 2019. This means the line could have around four or five years left to run.

During this period, more clarity will emerge about Tokyo’s plans to develop a new fighter – tentatively designated the F-3 – to replace its 96 Mitsubishi F-2 fighters. Should local F-35 production cease, an industrial base would be in place for this new programme.

Media reports have suggested that the additional F-35s will replace about 100 Boeing F-15s that are not viable for upgrading. Fleets Analyzer shows that the Japan Air Self Defence Force has 155 F-15Js and 45 F-15DJs, the average age of which is 30 years.

The 105 new F-35s will include 40 short-takeoff and vertical landing (STOVL) F-35Bs, which will operate from the Japan Maritime Self Defence Force’s pair of Izumo helicopter carriers.

Prior to Tokyo’s decision to obtain more F-35s, US President Donald Trump had called on Tokyo to invest “massive amounts” in US defence products.