WASHINGTON : The U.S. military has begun accepting certain F-35A aircraft without their next-generation AN/APG-85 radar installed, according to multiple defense reports and publicly available statements, as the Joint Strike Fighter program works through delays tied to its broader Block 4 modernization effort.
Deliveries of radar-less aircraft reportedly began in June 2025, affecting U.S. Air Force F-35A models from Lot 17 production onward. The F-35 Joint Program Office (JPO) has declined to confirm whether aircraft are being delivered without radars, but has acknowledged that current production jets are being built to accommodate the new APG-85 radar, which remains in development.
“F-35 Lightning II aircraft are being built to accommodate the F-35 advanced radar (APG-85) for U.S. Air Force, Navy, and Marine Corps,” a JPO spokesperson said in response to media inquiries. The office added that initial fielding of the APG-85 is planned for Lot 17 aircraft, with deliveries running through September 2026. Further details were withheld for security reasons.
Lockheed Martin, the prime contractor for the F-35 program, deferred questions to the JPO. Northrop Grumman, developer of the APG-85 radar, declined to comment.
Radar Integration and Structural Modifications
The AN/APG-85 is a key component of the Block 4 upgrade package and will replace the existing AN/APG-81 active electronically scanned array (AESA) radar currently fielded on operational aircraft.
While detailed specifications remain classified, the APG-85 is expected to incorporate gallium nitride (GaN) semiconductor technology, offering improvements in power efficiency, detection range, and electronic warfare performance compared to the older gallium arsenide-based APG-81. Like its predecessor, the new radar will support air-to-air and air-to-ground modes, synthetic aperture radar (SAR) mapping, and integration with the aircraft’s sensor fusion and electronic warfare architecture.
However, integrating the APG-85 requires physical modifications to the aircraft’s forward fuselage. Rep. Rob Wittman (R-Va.), Vice Chairman of the House Armed Services Committee and Chairman of its Tactical Air and Land Forces Subcommittee, confirmed that bulkhead configuration changes are necessary to properly position the radar array.
According to prior reporting, a mounting solution capable of accommodating both the APG-81 and APG-85 in the same airframe does not currently exist. Lockheed Martin has proposed redesigning the forward fuselage to allow either radar to be installed, with the revised structure potentially entering production in Lot 20 aircraft, currently projected for delivery between 2027 and 2028.
If adopted across all Partner and Foreign Military Sales (FMS) customers, the redesign would standardize the structure for both U.S. and allied aircraft using the APG-81.
Aircraft Delivered With Ballast in Place of Radar
Reports indicate that radar-less F-35As have been fitted with ballast weights in the nose to maintain proper center-of-gravity balance during flight. The aircraft remain airworthy and can operate alongside other F-35s equipped with radars.
Under the aircraft’s network-centric design, data is shared via the Multifunction Advanced Data Link (MADL) and Link 16. As long as at least one aircraft in a formation carries a functioning radar, other jets can receive radar-derived information through secure data links.
The aircraft also retains passive sensors, including the Distributed Aperture System (DAS) and the Electro-Optical Targeting System (EOTS), though these systems do not replace full radar functionality.
Without an onboard radar, an individual aircraft loses independent radar search capability and part of its electronic warfare capacity, as the radar contributes to both detection and electronic attack functions within the electromagnetic spectrum.
Power, Engine, and Thermal Constraints
The APG-85’s higher performance comes with increased electrical power demands. Public comments from Rep. Wittman indicate that the radar may require approximately 82 kilowatts of electrical power, exceeding the current margin available from the Pratt & Whitney F135 engine’s auxiliary power generation system.
In 2023, the Joint Program Office acknowledged that original engine power and thermal management margins had been under-specified. Upgrades to power generation and cooling systems are now underway, though they are also experiencing delays.
These issues are linked to Technology Refresh-3 (TR-3), a hardware and software upgrade required to enable Block 4 capabilities. TR-3 has faced developmental challenges, contributing to schedule slippage across the modernization effort.
Block 4 Cost Growth and Delays
The Block 4 upgrade program encompasses more than the APG-85 radar. Planned enhancements include:
- A new electronic warfare suite
- Replacement of the AN/AAQ-37 Distributed Aperture System
- Replacement of the Electro-Optical Targeting System
- Expanded data-sharing capabilities
- Upgraded onboard computing
- Improved thermal cooling capacity
In September 2025, the U.S. Government Accountability Office (GAO) reported that the Block 4 program’s projected cost had increased by approximately $6 billion and was at least five years behind schedule. The program had previously truncated certain early upgrades in an attempt to accelerate fielding, but delays have persisted.
The F-35 program has historically employed concurrency, allowing production to proceed while development and testing continue. While this approach maintains industrial throughput, it has resulted in multiple aircraft configurations and increased retrofit requirements across the fleet.
Foreign Customers Not Affected
Foreign operators currently receiving F-35 aircraft are reportedly unaffected by the APG-85 integration issue. Most international customers continue to receive aircraft equipped with the existing APG-81 radar.
The United States and 19 partner nations operate or are procuring the F-35. Japan has ordered 147 aircraft, South Korea 60, and Australia 72. Canada continues to finance its 88-aircraft order signed in 2023, though Ottawa has reviewed its procurement plans amid broader trade considerations.
Some partner nations have previously evaluated whether to adopt the full Block 4 upgrade package, given its cost growth and evolving timeline.
Industrial Considerations
Under typical aerospace manufacturing conditions, the absence of a major subsystem would halt production. However, stopping a high-rate production line carries significant financial and industrial consequences.
Continuing airframe production while deferring installation of a subsystem can preserve workforce stability, supplier networks, and international delivery schedules. Missing components are installed later during depot modifications or retrofit cycles.
Global supply chain constraints — including semiconductor availability, advanced materials, and skilled labor shortages — continue to affect defense production worldwide. Gallium nitride technology, central to modern radar development, relies on specialized fabrication processes and supply chains that remain under pressure.
Operational Implications
If radar-less aircraft are operationally deployed, they would be dependent on networked data from other platforms. While the F-35 was designed for cooperative operations, reliance on data links can impose tactical limitations, particularly in contested electromagnetic environments where communications may be degraded.
The absence of an onboard radar reduces independent engagement flexibility and diminishes electronic attack capability. However, aircraft retain passive sensing and off-board data access.
The long-term impact depends on how quickly the APG-85 reaches production maturity and how efficiently retrofit programs can be executed once integration challenges are resolved.
Broader Program Context
The F-35 remains the backbone of U.S. tactical aviation across the Air Force, Navy, and Marine Corps. It is the only fifth-generation fighter currently in large-scale Western production.
Maintaining production continuity while modernization upgrades mature reflects the complexity of evolving a fifth-generation aircraft in service while sustaining multi-service and multinational procurement commitments.
The timeline for full APG-85 fielding remains uncertain. Deliveries of Lot 17 aircraft are ongoing through 2026, with structural redesign options potentially entering production in Lot 20 beginning in 2027 or 2028.
How the Joint Program Office manages integration, retrofit, and engine power upgrades over the next several years will determine the pace at which the full Block 4 configuration becomes operational across the fleet.
——— End of Article ———
