The US Department of Defense is facing significant delays in its F-35 Joint Strike Fighter Block 4 modernization program, which is now projected to be completed no earlier than 2031, according to a recent report by the Government Accountability Office (GAO).
Block 4 was envisioned as a major upgrade package designed to enhance the jet with new weapons, advanced sensors, and improved electronic warfare systems. These upgrades are seen as essential for ensuring the aircraft can operate effectively against increasingly sophisticated air defenses.
However, the GAO report highlighted that costs have risen sharply, with expenses exceeding original estimates by more than $6 billion, while the program timeline has slipped by at least five years. Technical hurdles and production challenges have been the primary causes of these setbacks. To manage the situation, the F-35 Joint Program Office is restructuring Block 4 along with its Technology Refresh 3 (TR-3) upgrades into a new subprogram, a move directed by Congress in 2023 to tighten oversight.
TR-3, a $1.9 billion hardware and software package, has been the main source of delays in recent F-35 deliveries. In 2024 alone, Lockheed Martin delivered 110 aircraft, all averaging delays of more than 200 days. Pentagon planners expect to finalize new documentation by late 2025, which will clarify how many of the planned 66 Block 4 capabilities will actually move forward. The GAO cautioned that reduced scope and uncertain costs will remain concerns until a comprehensive estimate is completed.
