The United States Air Force (USAF) has reportedly refused to accept F-35 Lightning II fighter jets from the latest Lot 17 production batch that were delivered without onboard radars, adding a new layer of complexity to the already troubled Block 4 modernization effort.
While the USAF has declined to either confirm or deny reports surrounding the radar-less aircraft, multiple defense industry sources and media reports suggest that several F-35s delivered since mid-2025 were supplied without their primary radar systems due to ongoing technical delays associated with the next-generation AN/APG-85 radar.
The situation underscores mounting concerns about the pace, cost, and technical challenges surrounding the F-35 Joint Strike Fighter (JSF) program, led by Lockheed Martin, with key subsystems developed by Northrop Grumman and engine manufacturer Pratt & Whitney.
Until now, all operational F-35 variants — the F-35A for the USAF, F-35B for the US Marine Corps, and F-35C for the US Navy — have been equipped with the AN/APG-81 active electronically scanned array (AESA) radar, developed by Northrop Grumman. The APG-81 has been a cornerstone of the F-35’s sensor-fusion architecture, offering air-to-air tracking, air-to-ground targeting, electronic attack modes, and synthetic aperture radar (SAR) mapping.
However, beginning with Lot 17 production aircraft, the Pentagon had planned to introduce the more advanced AN/APG-85 radar as part of the sweeping Block 4 upgrade package.
The APG-85 represents a significant technological leap over its predecessor. While the APG-81 is based on gallium arsenide (GaAs) transmit/receive modules, the APG-85 uses gallium nitride (GaN) technology, offering substantially higher power density, greater thermal efficiency, improved resistance in contested electromagnetic environments, and extended detection ranges.
Yet integrating the APG-85 has proven far more complex than anticipated.
Unlike a simple component swap, the APG-85 requires an entirely new mounting structure within the F-35’s nose section. Defense Daily reported that since June 2025, newly produced F-35s have been delivered with updated mounting systems designed specifically for the APG-85.
However, because the new radar was not ready for integration, the aircraft were reportedly delivered without any radar installed. Instead, ballast weights were placed in the nose to maintain proper center-of-gravity balance.
This arrangement is believed to have applied only to US military deliveries. Foreign customers continue receiving F-35s fitted with the older APG-81 radar configuration.
In 2025, Lockheed Martin delivered a record 191 F-35 aircraft globally. It remains unclear how many of those were supplied to the US military without radars, and who authorized the acceptance of incomplete aircraft.
The core issue lies in power and thermal management. The APG-85 is estimated to demand approximately 82 kilowatts of electrical power — significantly higher than previous configurations. This requirement has cascading implications for the aircraft’s forward fuselage structure, cooling systems, internal power distribution architecture, and engine output.
Representative Rob Wittman, Vice Chairman of the House Armed Services Committee and Chairman of its Tactical Air and Land Forces Subcommittee, recently highlighted the issue in an interview with Defense Daily.
“The arrays on it [the APG-85] give it much more power, which is why we have to upgrade the engine,” Wittman said. “I think we need about 82 kilowatts of power versus what it’s producing right now.”
The radar integration challenge is closely linked to the Engine Core Upgrade (ECU) initiative for the F-35’s F135 engine, produced by Pratt & Whitney. The ECU is intended to increase thrust, improve cooling capacity, and support the higher energy demands of Block 4 systems.
However, the ECU itself has faced schedule slippages and budgetary scrutiny. Without the upgraded engine core, the F-35 may struggle to consistently generate the electrical output necessary to power the APG-85 and other Block 4 enhancements simultaneously.
The delay has reportedly forced the Pentagon to push full APG-85 integration from Lot 17 to Lot 20 production aircraft, creating a multi-year gap between airframe readiness and subsystem maturity.
Despite lacking a radar, sources suggest the radar-less F-35s are still airworthy and capable of functioning as operational aircraft under certain conditions.
The F-35’s design heavily emphasizes networked warfare and sensor fusion. Equipped with Multifunction Advanced Data Links (MADL) and other secure communications systems, F-35s can share targeting and situational awareness data in real time.
According to a defense source quoted by Defense Daily, radar-less F-35s can fly and operate effectively as long as they are accompanied by other F-35s equipped with the APG-81 radar. Through data-link connectivity, these aircraft can receive a shared battlefield picture, mitigating — though not eliminating — the absence of onboard radar.
In theory, such aircraft could be deployed in combat under emergency conditions. However, this approach carries elevated operational risks. Radar-equipped F-35s would need to radiate more frequently to compensate, potentially increasing their electromagnetic signature in high-threat environments.
The APG-85 was specifically designed to enhance detection against low-observable adversaries such as China’s Chengdu J-20 and Russia’s Sukhoi Su-57. Without it, the F-35’s long-range air superiority edge may be constrained in peer-level engagements.
The radar controversy is only one component of broader turbulence surrounding the Block 4 modernization program.
Originally envisioned as a sweeping capability expansion incorporating 66 new mission systems and weapon integrations — later expanded to more than 80 enhancements — Block 4 was initially slated for completion by 2026. That timeline was subsequently delayed to 2029.
In September last year, the Government Accountability Office (GAO) released a report warning that even after reducing the scope of the program, Lockheed Martin would require an additional two years to develop and field the revised improvements.
The GAO also reported that the cost of the Block 4 effort had increased by approximately $6 billion. Moreover, it cautioned that even a subset of the original capabilities might not be fully operational until 2031 — five years later than initially planned.
Beyond the APG-85 radar, Block 4 includes upgrades to the AN/AAQ-37 Distributed Aperture System (DAS), replacement of the Electro-Optical Targeting System (EOTS), enhanced electronic warfare capabilities, expanded weapons compatibility, improved navigation systems, upgraded mission computers, and expanded thermal management solutions.
The modernization effort is widely seen as essential to keeping the F-35 relevant against rapidly advancing adversaries, especially in the Indo-Pacific and European theaters.
The F-35 program has historically accepted aircraft in partial configurations, with the expectation that future upgrades would retrofit missing capabilities as technology matured.
Earlier production lots were delivered with limitations in software and weapon integrations, later corrected through upgrades. However, the current radar issue represents a more visible capability gap, as the radar is central to the aircraft’s core mission systems.
Defense analysts note that the decision to deliver radar-less aircraft may reflect industrial base pressures. Production lines cannot easily be paused without incurring massive cost penalties and disrupting global supply chains.
By delivering airframes configured for future radar installation, Lockheed Martin may be attempting to maintain production momentum while awaiting subsystem readiness.
Still, the optics are politically sensitive. Accepting multi-million-dollar fifth-generation fighters without one of their most critical sensors invites scrutiny from Congress and defense watchdogs.
The F-35 remains the backbone of US and allied tactical airpower for decades to come. More than 17 countries participate in the program, and global fleet numbers continue to rise.
For foreign customers, continued delivery of APG-81-equipped aircraft ensures no immediate capability shortfall. But for the US military — which intends to field the most advanced Block 4 configuration — delays could create a temporary mismatch between strategic ambition and operational reality.
The APG-85’s GaN-based architecture is particularly important for operating in contested electromagnetic environments, where adversaries deploy sophisticated jamming and anti-access/area denial (A2/AD) systems.
GaN radars are known for higher output power, improved signal clarity, and better thermal tolerance compared to GaAs systems. However, these advantages come with higher integration demands, explaining the cascading delays affecting both radar and engine upgrades.
It remains unclear when the APG-85 will be ready for operational installation on F-35 aircraft. Full integration likely depends on synchronized progress across radar production, engine upgrades, structural modifications, and software development.
Until then, the US military faces a delicate balancing act: sustaining production rates, managing modernization timelines, and ensuring combat readiness amid incremental capability gaps.
The radar-less F-35 episode illustrates the inherent risks of pursuing simultaneous cutting-edge upgrades across multiple subsystems in a complex fifth-generation aircraft.
As the Block 4 program moves forward, questions surrounding cost, timelines, and performance will likely intensify on Capitol Hill and within the defense community.
What remains certain is that the APG-85 radar is not merely an incremental improvement — it is a central pillar of the F-35’s future competitiveness against peer adversaries. Whether that future arrives on schedule remains an open question.
