The US stealth fighter jets and one of the Pentagon's latest grand investments, the F-35As, were rated as "operationally unready" 234 times over a year and a half since January 2021 in South Korea due to malfunctions, a South Korean lawmaker said on Tuesday.

People Power Party representative Shin Won-sik said that over the 18-month period, the fighters were grounded on 172 instances. The remaining 62 cases were due to the jets being able to take off but without being able to carry out certain missions.

The South Korean military should make strenuous efforts to both introduce such high-end weapons systems and maintain them, Shin added upon disclosing the data.

The multi-billion project's future is looking quite grim, with grounded fifth-generation fighters only being able to carry out missions for 12 days on average in 2021 and 11 days in the first half of 2022.

Over the same 18-month period, the older F-4E and the F-5 were only grounded 26 and 28 times, respectively.

The Air Force underlined that it had no problem with maintaining the readiness of the F-35As, with the aircraft meeting their target operational rate of 75%.

Seoul acknowledged that it had issues acquiring parts for defects identified in the F-35As, noting that it would be working on receiving them from the manufacturer within the shortest possible time frame.

South Korea finished deploying 40 F-35As in January under the country's first project aimed at acquiring Lockheed Martin's newest steal fighter.

Despite their low operational rates, stealth fighters have been gaining impetus since their introduction. The Swiss parliamentary committee on security policy in early September gave the green light to the purchase of 36 US-made F-35A fighter jets for the national army despite resistance from the country's opposition.

In late August, the Swiss government announced the impossibility of holding a referendum on the issue before the expiry of the US sales offers on March 31, 2023. The administration asserted that delaying the replacement of the fleet's 55 ailing planes would have detrimental effects on the country's security.

Germany, too, revealed in March that it would acquire 35 Lockheed Martin F-35s from the United States to upgrade its aging Tornado fleet, marking the first defense deal for the country since Chancellor Olaf Scholz's promise to spend some 100 billion euros on upgrading Germany's defensive capabilities in response to the war in Ukraine.

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The United States Air Force in late July even went as far as grounding its F-35A jet fleet, citing a potentially faulty component in the ejection seat that could endanger pilots in an emergency, a concern that has also grounded other types of military planes used for training.