The estimated per-plane cost to Japan of acquiring a single US F-35A stealth fighter soared by about 53 percent to US$137.6 million (14.7 billion yen) in FY 2017 from an estimated US$90 million (9.6 billion yen) in FY 2012, according to a report by the Asahi Shimbun.

Japan Defense Ministry officials attributed the catapulting price on the currency impact of a weaker yen. But some defense analysts blamed the surging costs on Japan’s procurement of the aircraft from the US government’s Foreign Military Sales (FMS) program.

Asahi noted FMS sales are considered part of the defense aid that the US provides to its allies. Because of this, buyers like Japan tend to pay the asking price, versus what might have been paid by purchasing the plane directly from Lockheed Martin, its manufacturer.

“As the F-35A is aircraft loaded with sensitive features, it is difficult to verify whether the cost is reasonable,” a senior Defense Ministry official was quoted as saying. “It is true that we tend to accept the US asking price.”

Asahi said Japan is expected to deploy a total of 42 F-35A advanced fighters in stages, starting from fiscal 2018, as a successor to its aging, US-made F-4 Phantom fighters.

Japanese Defense Minister Itsunori Onodera applauded the deployment of Japan’s first F-35A stealth fighter jet at the Self-Defense Forces’ Misawa Air Base on Saturday, citing the need for Japan to respond to growing threats posed by China and Russia.

“It is extremely significant to deploy the F-35A at a time when neighboring countries are rapidly modernizing and reinforcing the capabilities of their air forces,” Onodera said at the ceremony. “Equipped with high stealth features, the F-35A is among the most advanced in the world.”

The US F-35 development program has been plagued with cost overruns since its inception. Dubbed the world’s most expensive weapon, the price of developing the F-35 has risen to an estimated $406.5 billion, according to July data.

China is introducing the J-20, a stealth fighter with similar performance characteristics to the F-35A. Russia is also developing the Sukhoi Su-57.

The F-35A is the standard takeoff version of the US fighter.