U.S. F-35 fighter jets were available to fly only half the time in 2024 due to maintenance shortcomings by Lockheed Martin (LMT.N), a report from the Defense Department's Office of the Inspector General said.

The availability of F-35 aircraft in 2024 was 50 percent, 17 percent below the minimum performance requirement, the Pentagon watchdog said.

According to the report, the average availability rate was because "(the Pentagon) did not always hold Lockheed Martin accountable for poor performance related to F-35 sustainment."

The report attributed the problem to inadequate oversight by the Department of Defense, despite contractual obligations. Auditors found that even with such low availability rates, the Pentagon paid Lockheed Martin about $1.7 billion without imposing any financial penalties.

The F-35 program is also plagued by severe delivery delays and cost overruns. A report released in September by the U.S. Government Accountability Office (GAO) in September found that most F-35 aircraft delivered in 2023 by Lockheed Martin and engine maker Pratt & Whitney were late, with an average delay of 61 days. All more than 100 aircraft delivered in 2024 were delayed, with an average delay of 238 days.

The report also noted that as of December 2023, the total procurement cost of the F-35 program had exceeded $485 billion, up nearly 10 percent from the $442 billion estimate in December 2022 and more than double the original cost projection made in 2001.

This year, countries including Canada, Switzerland and Spain have either reviewed their F-35 procurement plans or reduced or even abandoned their purchases. The aircraft's complex maintenance system has also affected allied readiness. According to reports from the UK on Wednesday, three Royal Air Force F-35B jets have been sent back to the United States for inspection after long-term deployment in high-salinity, high-humidity, high-temperature environments with strong ultraviolet exposure raised concerns about possible internal corrosion.

(With input from Reuters)