Critical F-35 Block 4 Upgrades Face Further Serious Issues and Delays

Efforts to modernise the F-35 fifth generation fighter to the Block 4 standard have faced mounting delays, with two further years needed to develop and install planned improvements despite significant reductions to the scope of upgrades, according to a new report from the Government Accountability Office. The report was based on an audit of the F-35 program conducted by the office, and follows two decades of serious delays and shortcomings with the program, and a long history of watering down performance requirements to reduce the extend of delays. Block 4 now will “have fewer capabilities, will experience schedule delays, and will have unknown costs,” the report noted, stressing that “Block 4 will now consist of “a subset of the original 66 … capabilities and those added in later years.” These delays come at a time when advances in Chinese air power have made the enhancement of the F-35’s capabilities an increasingly urgent priority.

According to the Government Accountability Office’s report, the F-35 program is still struggling to complete testing of the long delayed Technology Refresh 3 effort, which provides processing power and software needed for Block 4’s enhancements. “According to program officials, Lockheed Martin plans to begin delivering combat-capable aircraft with the TR-3 that will enable Block 4 capabilities in 2026, a three-year delay, due to hardware and software issues,” the office’s reported noted. It added that “supply chain challenges continue to strain” aircraft and engine production schedules, “leading to increasingly late deliveries.” The full capabilities intended to be achieved by the F-35 Block 4 were initially intended to be achieved in the mid-2020s, but have been postponed to the early 2030s. A Director of Operational Test and Evaluation report in early 2025 concluded that the F-35 “continues to fall short” of the metrics set for it in the original Capabilities Development Document, noting that “improving and sustaining improvement in aircraft suitability metrics is difficult to achieve.”

The F-35 program’s future has become increasingly uncertain as both China and the United States appear poised bring their first sixth generation fighters into service in the 2030s, with China having became the first country in the world to unveil a sixth generation fighter, with footage released on December 26 having shown aircraft from two such programs at advanced prototype stages. Both have since been test flown both intensively, and are expected to enter service near the beginning of the next decade. The stock value of the F-35’s primary contractor Lockheed Martin notably suffered in the aftermath of the Chinese fighters’ unveiling specifically due to the significantly possibility that this would reduce demand for the F-35, which would be left a generation behind.

The expectation of serious delays to and issues with the development of America’s own sixth generation fighter, the F-47, has led Lockheed Martin to pitch an enhanced ‘5+ generation’ variant of the F-35 integrating a range of sixth generation technologies as an alternative. Serious shortcomings with all prior efforts to significantly enhance the F-35, including delays to efforts to bring it up to the Block 4 standard, raise a significant possibility that efforts to implement more ambitious upgrades as proposed by the firm will not be considered viable. The future of the F-35 program has particularly significant implications for the balance of power across multiple theatres, as not only is it by far the largest weapons program in world history, but it is also the only fighter of its generation in production on a meaningful scale outside China, and with comparable capabilities to the Chinese J-20 and J-35 fifth generation fighters.