The most expensive weapons programme in history may soon deliver fighter jets without radars. Block 4 development delays have pushed the F-35’s next-generation APG-85 radar so far behind schedule that new production aircraft could roll off the Lockheed Martin assembly line in Fort Worth missing the single most important sensor in a modern fighter. It sounds like satire. It is not. The F-35 Joint Programme Office is quietly confronting a timeline collision: production lines that cannot stop and a radar that is not ready. The result could be jets that fly — but cannot fight.

How Did We Get Here?

Block 4 is the F-35’s planned leap from a capable fighter to a dominant one. It includes the APG-85 radar (with significantly greater bandwidth, range, and electronic warfare capability than the current APG-81), new electronic warfare systems, integration of next-generation weapons like the AIM-260 JATM, and the Technology Refresh 3 (TR-3) hardware package that underpins everything.

TR-3 has been the bottleneck. The new core processor and memory systems required to run Block 4 software have been plagued by stability issues. Lockheed has been delivering TR-3 hardware aircraft since late 2024, but many sit at Fort Worth in a condition the Pentagon calls “limited functionality” — unable to perform combat missions until the software catches up. The APG-85 depends on TR-3 working flawlessly. If TR-3 software continues to slip, the radar cannot be integrated — and jets coming off the line will either be delivered with the older APG-81 or, in a worst case, with radar bays prepared for the APG-85 but no radar installed.

The Production Line Cannot Wait

Lockheed Martin produces roughly 156 F-35s per year for the United States and international partners. Stopping the line would be catastrophically expensive — hundreds of millions per month in fixed costs alone, plus contractual penalties for late deliveries to allies who have already paid. The Pentagon’s solution has historically been to deliver aircraft in a less-than-complete configuration and retrofit them later — a practice known as “concurrency.” It is how the F-35 programme has operated since its earliest days. But delivering fighters without a working radar is a new frontier, even for a programme accustomed to delivering first and fixing later.

What It Means for the Fleet

The immediate impact falls on the U.S. Air Force, Navy, and Marine Corps, plus international operators who are counting on Block 4 capability. Countries like Finland, Switzerland, and Canada have made procurement decisions based on Block 4 specifications. Delivering them Block 3F aircraft — or worse, radar-less airframes — would be a political and strategic embarrassment. The F-35 remains the most capable multirole fighter in production anywhere in the world. Its sensor fusion, low observability, and networked warfare capabilities are unmatched. But a fighter without a radar is a sports car without an engine — it looks the part, but it cannot do the job. The programme office says it is working to avoid the worst-case scenario. The question is whether the schedule agrees.

Sources: The War Zone, Air & Space Forces Magazine, Defense News