Starting this fall, every new F-35 Lightning II delivered to the United States military will carry a weighted ballast in the nose where its fire-control radar should be. The aircraft will be airworthy. They will not be combat-ready. And depending on how long delays continue, more than 100 jets could enter the inventory in this state — training assets masquerading as frontline fighters at a moment when the Pentagon faces its most demanding strategic environment since the Cold War.

The proximate cause is a structural incompatibility between the new AN/APG-85 radar, developed by Northrop Grumman as the cornerstone of the F-35's Block 4 modernization, and the redesigned forward fuselage bulkhead introduced in Lot 17 production. The two systems were engineered in parallel. The airframe won the race. The radar did not.

As Breaking Defense first exclusively reported on March 19, 2026, the Marine Corps is expected to become the first service to accept F-35Bs without radar, followed later in 2026 by the Air Force and Navy with their F-35A and F-35C variants, respectively. Rep. Rob Wittman (R-Va.), chairman of the House Armed Services Committee's Tactical Air and Land Forces Subcommittee, confirmed the situation publicly, telling reporters: "Right now, they're going to be produced with ballasts, which creates an aircraft that's not going to be combat-coded anytime soon."

■ Program Data At A Glance — F-35 / APG-85

> $2.0 Trillion (77-year estimate)
$485+ Billion (Dec. 2023)
$10.6B → $16.5B (+$6B gap, 2021 est.)
≥ 5 years (completion ≥ 2031)
238 days (all 110 aircraft late)
Lot 17 (deliveries began 2025)
Lot 20 (deliveries begin 2028)
Hundreds of millions — despite late delivery

The Engineering Root Cause

To understand the current impasse, one must understand the forward fuselage bulkhead — the structural component that positions and aligns the radar array within the nose of the aircraft. The alignment matters enormously: it establishes the physical attitude of the antenna face, which determines the precision and geometry of the radar beam. Wittman put it plainly: "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."

The APG-81, which has equipped all operational F-35s since the program's early production lots, uses one bulkhead geometry. The APG-85 uses a different one. When the program committed to introducing the new radar beginning with Lot 17, the airframe was physically redesigned to accept the new sensor. That committed the production line to a configuration that cannot accept the older radar as an interim solution — there is no plug-and-play fallback. As one industry source told Defense Daily, aircraft delivered since June 2025 have "APG-85 mountings, which do not fit the APG-81."

The result: jets rolling off the Lockheed Martin production line in Fort Worth with a nose ballast weight to replicate the center-of-gravity contribution of the missing radar. The aircraft can fly. They can even operate in a limited sense alongside radar-equipped jets, receiving targeting data via the F-35's Multifunction Advanced Data Link (MADL) and Link 16 datalinks. But they cannot function independently as combat aircraft. Stacie Pettyjohn, director of the defense program at the Center for a New American Security, characterized an aircraft without a radar as "very near-sighted," noting that while off-board datalinks provide some situational awareness, doing so "would come with some latency and the risk of an enemy jamming communications channels."

"Lots of aircraft out there, but not ones that are ready to go to the fight."

— Rep. Rob Wittman (R-Va.), Chairman, HASC Tactical Air & Land Forces Subcommittee, March 2026

What the APG-85 Was Supposed to Deliver

The stakes of this delay cannot be separated from an understanding of what the APG-85 is meant to accomplish. The new sensor represents a generational transition in active electronically scanned array technology, moving from the gallium arsenide (GaAs) transmit/receive modules of the APG-81 — whose design heritage traces to the 1990s — to a gallium nitride (GaN) architecture that delivers substantially higher power density, improved thermal efficiency, and extended detection range against low-observable targets.

The APG-85 is expected to demand approximately 82 kilowatts of power — a figure that itself drives the separate and also-delayed Engine Core Upgrade (ECU) for the Pratt & Whitney F135 engine. It is designed to provide long-range detection and tracking of aircraft, missiles, and unmanned systems; high-resolution synthetic aperture radar (SAR) ground mapping for targeting and bomb damage assessment; enhanced electronic countermeasures resistance through low probability of intercept/low probability of detection (LPI/LPD) waveform design; and offensive electronic attack capability specifically oriented toward countering integrated air defense networks of the type fielded by China and Russia.

Pettyjohn underscored the strategic dimension: "F-35s have performed really well in the Middle East and in Venezuela against lesser adversaries. But when it comes to countries like China that have built truly integrated air and missile defenses, sophisticated air forces with significant air-to-air capacity, that would be a really stressful test, and they need to continue to advance the capabilities that were initially put into the F-35 to remain relevant." The APG-85 is, in essence, the specific system intended to make that advance possible. Without it, new Lot 17 and Lot 18 aircraft are technologically inferior to the very jets they were meant to replace.

Certification Time: The Operational Driver

Wittman, who has been conducting monthly phone calls with the F-35 Program Executive Officer — currently Marine Lt. Gen. Gregory Masiello, who assumed the role in July 2025 — identified radar certification time as a primary driver of the slippage. "The APG-81 could be certified in three days," he told reporters at the McAleese and Associates conference. "The newer radar takes much, much longer." Northrop Grumman has shortened the test cycle, he acknowledged, but not enough: "They're not doing that at the pace necessary for the aircraft coming off the line."

The certification requirement reflects genuine technical complexity. The APG-85's GaN-based transmit/receive modules — estimated at more than 2,400 individual elements — require extensive functional and electromagnetic compatibility validation before the radar can be cleared for flight on a stealth aircraft. The radar's LPI/LPD emission characteristics must be verified not to compromise the aircraft's signature. Its integration with the F-35's distributed sensor architecture, including the Distributed Aperture System and Electro-Optical Targeting System, must be validated through a multi-mode test regime. These are not bureaucratic delays; they are engineering imperatives. But planning them in parallel with an aggressive production schedule — rather than sequencing them appropriately — created the current crisis.

The Broader Block 4 Catastrophe

The APG-85 situation cannot be understood in isolation. It is one of multiple concurrent failures within the F-35's Block 4 modernization program — an effort that the Government Accountability Office, in its September 2025 report to Congress, characterized bluntly: "The F-35 program continues to overpromise and underdeliver."

Block 4 was originally conceived as a package of more than 66 discrete capability improvements, underpinned by a $1.9 billion hardware and software package called Technology Refresh 3 (TR-3), which provides the processing backbone — reportedly up to 37 times more computational throughput and 20 times more memory than its predecessor — needed to run advanced sensor fusion, weapons integration, and electronic warfare modes. TR-3, which was originally due in April 2023, has been beset by immature integrated core processor designs, Next Generation Distributed Aperture System delays, and software stability issues ranging from radar malfunctions to cockpit display failures. In 2024, operational testing of TR-3 software on the F-35 was reported as unlikely to commence before 2026.

As of the GAO's September 2025 assessment, Block 4 will not be complete until at least 2031 — at least five years behind the original schedule. The program has reduced the number of capabilities it will deliver, deferred those dependent on the Engine Core Upgrade until at least 2033, and eliminated others entirely as "no longer meeting warfighter needs." Block 4 costs had already grown from a $10.6 billion baseline to $16.5 billion as of 2021, with an updated cost estimate — expected in fall 2025 — still not publicly confirmed. The engine upgrade itself is now not expected to enter production until 2031, pushing full Block 4 capability with enhanced power and cooling to the mid-2030s at the earliest.

■ Delay Timeline: Key Events

  • 2001 F-35 program baseline established; acquisition cost projected at $233 billion.
  • 2012 Program rebaselined after costs breach statutory thresholds; estimate rises to $396 billion.
  • Jan. 2023 Northrop Grumman officially announces APG-85 development contract.
  • Apr. 2023 TR-3 software originally due; not delivered. Delivery halt follows.
  • July 2023–July 2024 Year-long freeze on new F-35 deliveries due to TR-3 delays.
  • Dec. 2024 Lot 18 contract awarded as undefinitized deal for 145 jets (83 U.S. military).
  • Mar. 2025 Lockheed CEO Taiclet warns of APG-85 schedule risks in letter to USAF chief; proposes new dual-compatible bulkhead design.
  • June 2025 F-35 deliveries with APG-85 bulkheads begin — without APG-85 radars.
  • Sep. 2025 GAO: Block 4 delayed ≥5 years, $6B over budget; all 2024 deliveries averaged 238 days late.
  • Sep. 2025 Lots 18–19 contract finalized; Lot 19 includes 69 U.S. military jets.
  • Fall 2026 All new U.S. F-35 deliveries (A, B, C variants) expected without radar per Breaking Defense report.
  • 2028 (est.) New dual-compatible bulkhead expected with Lot 20; APG-85 fielding may begin if program stays on revised schedule.

The Contractor Accountability Problem

Perhaps most damaging to program credibility is the incentive fee structure exposed by the GAO. Between 2021 and 2024, Lockheed Martin and Pratt & Whitney collected hundreds of millions of dollars in performance incentive fees even as delivery performance deteriorated. All 110 aircraft Lockheed delivered in 2024 arrived late — by an average of 238 days, nearly four times worse than the 61-day average lateness recorded in 2023. Pratt & Whitney delivered all 123 engines late in the same year. Yet contract structures permitted partial fee payments for jets delivered up to 60 days late, and when no aircraft met even that threshold, program officials redirected more than $100 million in unearned incentives to cover lab upgrades and TR-3 repairs rather than withholding them.

"Unless the F-35 program re-evaluates its use of incentive fees and better aligns them to achieving desired production schedule outcomes, it will be at greater risk of continuing to reward contractors for delivering engines and aircraft late," the GAO stated. The watchdog's conclusion is stark: the fee structure is "largely ineffective at holding the contractors accountable."

In this context, the decision to accept radar-less aircraft — allowing the production line to continue generating revenue for Lockheed Martin while the government absorbs the operational risk of non-combat-capable jets — is entirely consistent with the established pattern. The F-35 Joint Program Office noted that "the program in coordination with the Services deliberately undertook a highly concurrent development and production program" and that "this decision was made with full understanding of the risk." That may be accurate. The question is whether understanding a risk and appropriately managing it — including its financial implications for the contractor team — are the same thing.

Strategic Implications: A Shrinking Combat-Ready Fleet

The immediate tactical impact of radar-less deliveries is partially mitigated by the fact that, since July 2024, all new F-35 deliveries have already been non-combat-coded due to the unresolved TR-3 software situation. Combat operations — including strikes in the broader Middle East region — have continued with older TR-2 software jets from earlier production lots. In that sense, the addition of a radar gap to an already-existing software gap does not immediately reduce the number of combat-available aircraft.

The longer-term picture is considerably more troubling. As Pettyjohn noted, having to retrofit a large number of aircraft with the APG-85 at a later date "would be a huge blow to the tactical aircraft fleet, which is shrinking right now." Retrofit timelines and costs are presently unknown. The Air Force has already substantially cut its F-35 procurement plans, targeting just 39 aircraft in FY2027 and as few as 18 in FY2028 — reflecting a judgment that pre-Block 4 aircraft represent diminishing returns against peer threats. Aircraft without combat-capable software and without a radar compound that calculus. "Then we're starting to see where the numbers are going to belie the real capability that is available at any moment in time," Pettyjohn observed.

Foreign buyers of the F-35 are not affected. The APG-85 has not been cleared for export, and international customers continue to receive aircraft fitted with the APG-81. This divergence — where allied air forces are flying fully-equipped F-35s while U.S. forces take delivery of radar-less airframes — is a public relations and alliance management problem of the Pentagon's own creation.

The View From History: The Tornado F.2's 'Blue Circle Radar'

For any student of defense procurement, the F-35's radar-less deliveries carry an uncomfortable echo. In 1984, the Royal Air Force took delivery of the first production Panavia Tornado F.2 air defense variant — an aircraft designed specifically to intercept Soviet bombers, whose central capability was the GEC-Marconi AI.24 Foxhunter pulse-Doppler radar. The radar, several years late and 60 percent over budget, was not ready. The aircraft were delivered with concrete and lead ballast in the nose cones to maintain center-of-gravity balance.

RAF crews, in the tradition of British military dark humor, promptly named the missing sensor the "Blue Circle radar" — a play on the Blue Circle cement brand and the Rainbow Code naming convention used for British military avionics. The ballast was not merely an embarrassment. The first batch of 18 Tornado F.2s were restricted to training use, and the Foxhunter only entered service in 1985 in an interim standard that still did not meet requirements. A full capability standard was not achieved until the 1990s. The aircraft never fully exploited the capabilities of the AMRAAM and ASRAAM missiles it eventually carried.

The structural parallel is precise: a new airframe committed to a sensor that was not ready; an incompatible prior sensor that could not be substituted; ballast in the nose; training-only operations; unknown retrofit costs. Forty years of procurement reform, multiple generations of program management doctrine, the creation of the Office of the Director of Operational Test and Evaluation, the institutionalization of Milestone Decision Authority oversight — and the United States is in 2026 reproducing, at a scale 10 times larger and a cost several orders of magnitude greater, the same failure mode as the RAF in 1984.

"The bulkhead conversation should've been had years ago."

— Anonymous source familiar with the F-35 program, March 2026 (Breaking Defense)

The Path Forward — and Its Uncertainties

The near-term mitigation path is narrow. The F-35 Joint Program Office has stated that it has "plans to accelerate APG-85 production capacity," but details remain classified. In the best case, the radar reaches production maturity during the Lot 18 production run, limiting the number of ballast-nosed aircraft to a relative handful. In a more likely scenario, based on the program's historical trajectory, delays persist through Lot 19, potentially affecting the 69 U.S. military aircraft in that contract.

Lockheed Martin CEO Jim Taiclet acknowledged the risk formally in a March 2025 letter to then-Air Force Chief of Staff Gen. David Allvin, warning of schedule risks and committing to a redesigned forward fuselage that could accommodate either the APG-81 or APG-85. That dual-compatible bulkhead is not expected until Lot 20, whose deliveries begin in 2028. Even then, the redesign will require re-certification and integration testing — which itself could extend into the early 2030s for a full program-wide retrofit.

Wittman expressed confidence that the issue will eventually be resolved — but only eventually: "With the new radar, there's only so much that you can do to compress the time frame, just because of the rigor necessary in certifying a new radar system, a radar system that's much more capable, which the aircraft needs." That is a measured and technically accurate statement. It is also, from the perspective of operational commanders who need combat-ready aircraft today, cold comfort.

The APG-85 delay is, in the end, a symptom. The disease is a $2 trillion program whose acquisition strategy has for two decades prioritized industrial continuity and contractor revenue over the delivery of combat capability. The GAO has documented this for twenty years. Congress has been briefed. Corrective action requests have been issued. Incentive fees have been paid. And the jets, one by one, roll off the line with lead in their noses where their eyes should be.