The status of the F-35’s new AN/APG-85 radar has always been shrouded in secrecy – until Marine Corps Lieutenant General Gregory Masiello, head of the F-35 Joint Program Office (JPO), admitted to the Senate Armed Services Committee that six F-35Bs had been accepted by the USMC without their radars fitted. This figure is believed to represent the tip of an iceberg.
When the Royal Air Force (RAF) decided to re-role its Canberra T.Mk 11s for target facilities under the new designation T.Mk 19, these aircraft (previously used for training Javelin night fighter radar operators) had their maintenance-intensive radars removed and replaced by concrete ballast. In those days British weapons and avionics systems had colour-based codenames and the ballast was sarcastically dubbed ‘Blue Circle’ (after the name of the well-known UK cement manufacturer). Later, when Tornado F.Mk 2s were delivered without their planned AI24 radar, they were frequently described as being equipped with ‘Blue Circle’ radars, although in the case of the F.Mk 2 the ballast was actually in the form of metal bars.
Now, it has been officially acknowledged that new Lockheed Martin F-35 Joint Strike Fighters are being delivered to the US services without a radar. This is understood to be a result of development delays to the new AN/APG-85 radar, which requires a new forward fuselage bulkhead. Expecting the radar to be fielded some time ago, Lockheed Martin started building aircraft for the US services with the new bulkhead, which cannot accept the original AN/APG-81 radar. The problem does not affect F-35s being built for export customers, since the APG-85 is not currently available to them.
Rob Wittman, a Republican Congressman from Virginia who is Vice Chairman of the House Armed Services Committee and Chairman of its Tactical Air and Land Forces Subcommittee, noted that the APG-85 required physical alterations to the F-35’s bulkhead. In an interview with Defense Daily on 3 February 2026 he said, “The bulkhead configuration is key because for both of the radars, they are very different. Remember, the bulkhead configuration allows the placement of the radar towards the attitude of the array, and the attitude of the array makes all the difference in the world about how the radar operates.”
Existence of the APG-85 was first revealed in US Air Force (USAF) budget documents in 2022, while Northrop Grumman acknowledged that it was developing the new radar as the replacement for the APG-81 on 11 January 2023. The APG-85 is expected to form the “cornerstone” of the F-35’s future sensor suite and represents a critical component of the aircraft’s wider Block 4 upgrade.
Northrop Grumman described the APG-85 as an “advanced multi-function sensor that will be compatible with all variants of the F-35 aircraft”, which it said would “be capable of defeating current and projected adversarial air and surface threats”.
The F-35 Joint Program Office (JPO) emphasised from the start that “certain information will continue to be protected by enhanced security measures due to the critical nature of the technology”. It is known, though, that the APG-85 will leverage decades of advancements in active electronically scanned-array (AESA) radar technology, including the exploitation of gallium nitride (GaN) transmit/receive modules. The original APG-81 used gallium arsenide (GaAs) technology.
The APG-85 is expected to be more powerful than the APG-81, thanks to the use of GaN, with implications for radar performance. It may also improve the F-35’s electronic attack capabilities, giving an improved ability to transmit narrow beams of microwave energy to jam or even damage enemy emitters.
The JPO originally said the new radar was “planned for fielding in Lot 17”. In June 2025 the Pentagon insisted that the new radar would be ready for Lot 17, although Breaking Defense reported that Jim Taiclet, the CEO of Lockheed Martin, had warned then Air Force Chief of Staff General David Allvin that there were risks in the radar’s delivery schedule.
Some 126 F-35s were authorised in Lot 17, for the US forces, international partners and Foreign Military Sales (FMS) customers. Lot 17 aircraft were originally due to be delivered by late 2025 or early 2026, but began delivery in 2025 and deliveries will now continue through to September 2026. Reports that all Lot 17 aircraft for the US services (starting in June 2025) would be delivered without radars appear to be wrong, with the USAF explicitly denying it had received F-35As without radars in February 2026.
Air & Space Forces Magazine reported that the new APG-85 radar would probably be available in time to equip seven aircraft “at the tail end of the Lot 17 F-35 contract”. These may include the six radarless F-35Bs that Marine Corps Lieutenant General Gregory Masiello, head of the F-35 JPO, told the Senate Armed Services Committee about. Lt Gen Masiello told Senator Mark Kelly, an Arizona Democrat and a retired naval aviator, “We have accepted six aircraft for the Marine Corps that do not have a radar installed,” confirming that this was due to a lack of available APG-85 radars.
The first of these F-35Bs flew an acceptance flight with ballast rather than a radar in the last week of February 2026.
This would imply that the new bulkhead was embodied at the tail end of Lot 17 and became standard on US customer aircraft produced in Lots 18 and 19, which were finalised in late 2025. The USD 24.3 billion (EUR 21.23 billion) Lot 18/19 contract covers the delivery of 296 F-35s, 148 of them in Lot 18, beginning this year.
The 148 aircraft in Lot 18 include 40 F-35As for the USAF, nine F-35Cs for the US Navy and 12 F-35Bs and eight F-35Cs for the US Marine Corps. The same totals apply to Lot 19. Lot 18 and 19 deliveries are scheduled to wrap up in around August 2028.
This would suggest that more than 138 F-35s will be built with the fuselage bulkhead for the APG-85, which is not scheduled to be delivered before 2028. This means that up to 138 F-35s (plus at least seven Lot 17 aircraft) will be delivered without a radar.
Mitigation of this shortfall is proving difficult.
When Taiclet wrote to Gen Allvin in June 2025, he offered to redesign the aircraft’s forward fuselage to be capable of accommodating either the APG-81 or the new APG-85 radar in order to “to mitigate potential delays” and in order to take “proactive steps to create viable options for Lot 20 aircraft if necessary”. Lockheed Martin confirmed that the revised fuselage design could be incorporated into Lot 20 production, which was then estimated to begin between 2027 and 2028.
It is not known whether the proposal was accepted.
The JPO noted, “The Department of War deliberately undertook a highly concurrent development and production program for Block 4 capabilities (Technical Refresh 3 (TR-3), APG-85, etc) and the largest fighter aircraft production line in the world. DoW officials made this decision with full understanding of the risk of having production aircraft ready ahead of the Block 4 capabilities. The services’ decision ensured that production aircraft could accept Block 4 capabilities, rather than continuing to build Block 3 F-35s that would require extensive retrofit for Block 4 capabilities, thereby saving multiple years of retrofit hardware installation.”
The F-35s delivered without radars are fully airworthy and may have some limited usefulness for training, since they can still access the radar picture provided by other APG-81-equipped F-35As via the Multifunction Advanced Data Link (MADL). They lack electronic warfare (EW) capabilities, however, and would be highly reliant on their wingmen. “I don’t think I would count them as fully mission capable,” Gen Masiello conceded.
Even when APG-85 sets are finally being delivered, the F-35’s radar issues will not be over.
The Block 4 upgrade will require more power and more cooling. To enable this Pratt and Whitney is developing an ‘Engine Core Upgrade’, while the aircraft’s cooling system, the Power and Thermal Management System (PTMS), will also need to be upgraded. The current Honeywell Aerospace PTMS is an integrated system that combines the auxiliary power unit, emergency power and environmental control into a single architecture. It produces about 30 kW of cooling capacity, whereas the APG-85 and Block 4 upgrade will require up to 80 kW of cooling. Lockheed Martin has launched a competition to find a new system.
Honeywell has proposed a scalable, two-phase upgrade. The first phase is a software-only upgrade that boosts cooling capacity to 40 kW, reducing bleed air usage by up to 41%, reducing the load on the F135 engine and lowering overhaul costs. Phase 2 incorporates hardware and software enhancements, including improved heat sinks and fluid management in the liquid cooling loop. These will push the capacity of the PTMS to deliver 62-80 kW of cooling capacity.
Collins Aerospace (RTX) is offering a new, next-generation power and thermal management system known as the Enhanced Power and Cooling System (EPACS). Collins has successfully tested a fully functional demonstrator of EPACS, which is already capable of producing 80 kW of cooling and is assessed as having reached Technology Readiness Level 6, making it ready for engineering and manufacturing development (EMD).
The JPO has said that a new cooling system solution should be ready to field in about 2032, after selection in 2027, although some sources suggest that the F-35 programme is not planning to start production of a new power thermal management unit (PTMU) until 2033. Until then, the APG-85 will not be able to be used at anything like full power.
Delivering F-35s without radars marks a new low for what has been a troubled F-35 programme, but the delivery of aircraft with limited capability is nothing new. There was a year-long gap in F-35 deliveries from July 2023, when it became clear that the Technology Refresh 3 (TR-3) upgrade was unfit for service, with its software unreliable and unstable.
The TR-3 upgrade was intended as enabler for the Block 4 modification, providing a new ‘computing backbone’ for the F-35, providing 25 times more computing power than the existing TR-2 architecture and including new displays as well as a replacement core processor and memory unit.
Between 90 and 120 aircraft were built to TR-3 standards and delivered straight to storage, with the US Department of Defense (DoD) refusing to accept them. The US DoD initially planned to delay accepting aircraft until they were combat capable, but a compromise was agreed under which the TR-3 software would be introduced in phases, with the JPO withholding a portion of delivery payments (about USD 5 million per aircraft) until TR-3 combat capability was “qualified and delivered”.
TR-3 software was initially installed in a ‘truncated’ form. The first release (40P01) was stable, capable and maintainable enough to allow combat training, with full combat capability waiting for the second software release (40P02). The TR-3 in truncated form missed some of the capabilities that were already available on older TR-2 aircraft and the training value of TR-3 aircraft was limited by a lack of commonality with TR-2 software.
In June 2025 a senior Lockheed Martin executive, J R McDonald, the company’s vice president of business development for the F-35 programme, said “We believe we have reached that point” where an upgrade known as TR-3 could officially support F-35 combat capabilities, although he admitted that “a single [unspecified] combat capability remains to be validated by the US government”. Some 200 TR-3 aircraft had been delivered by that point.
McDonald said that he could not offer a date for when “final closure with the US government” would be achieved or when the process would be completed, but said that “We think we’re very close to that”.
However, persistent software instability has meant that no F-35 aircraft configured with TR-3 hardware and software is combat-capable thus far, with these aircraft restricted to training and testing duties. No combat-capable TR-3-configured F-35s were delivered during FY2025 and in early 2026 the US DoD’s Director of Operational Test and Evaluation (DOT&E) confirmed that none of the 158 TR-3 aircraft delivered to the DoD were combat-capable. Some sources suggest that full combat capabilities will not be available before 2031.
The situation has not been helped by problems with what was planned to be the last version of the TR-2 software (30R08). This proved to be “predominantly unusable” for OT&E events during most of FY25, even after nearly three years of development testing. Dedicated OT&E with 30R08 software began in September 2025 but stability problems, capability shortfalls and the discovery of deficiencies rendered it unfit for service at that point.
The coming Block 4 upgrade is even more troubled, but that is better described separately.
