WASHINGTON — The F-35 Joint Program Office and manufacturer Lockheed Martin on Wednesday said the first fighters upgraded with new capabilities may not be delivered until at least April 2024, and possibly as late as next June.

This means the delivery of fighters with a slate of improvements known as Technology Refresh 3, or TR-3, will be at least a year behind schedule. And it could mean nearly an entire year’s worth of F-35s — perhaps up to 150, if production rates continue at full pace — could be parked at Lockheed Martin facilities until the company can deliver them.

TR-3 is intended to give the aircraft better displays, computer memory and processing power, and is necessary before a more expansive modernization effort, dubbed Block 4, can be added to the fighter. It was originally due in April 2023.

Problems with TR-3′s hardware and software caused its development to slip behind. In a March hearing, the F-35 program executive officer, Lt. Gen. Michael Schmidt, first said TR-3 would arrive in April 2024.

The F-35 Joint Program Office earlier this year said hardware issues had been addressed. But the office later said in June that software issues remained with TR-3, and getting its programming to work with the new hardware was proving difficult.

Lockheed Martin began rolling the first new TR-3-enabled F-35s off its Fort Worth, Texas, production line in July. But because the software remains unfinished, those fighters cannot participate in check flights that are necessary for the Defense Department to accept delivery. Lockheed is now storing these F-35s at Fort Worth.

In June, when the JPO announced the planned delivery halt, it said it expected TR-3 to be ready between December 2023 and April 2024.

JPO spokesman Russ Goemaere said in a Wednesday email to Defense News that it has continued to update U.S. military leaders, international partners and foreign governments purchasing the F-35 “about the progress and challenges observed in testing TR-3 software in flight.”

But, Goemaere added, the TR-3 program still has risks.

“Since our testimony to Congress in March 2023, we have made significant progress in the TR-3 program, but have also experienced challenges with TR-3 software maturity during flight test,” Goemaere said. “Given remaining risk in the TR-3 program, we have updated our forecast for the first delivery of a TR-3 configured F-35 to the time frame between April 2024 through June 2024. We continue to work very closely with industry partners, particularly Lockheed Martin, to address program risk and deliver TR-3 to warfighters.”

Lockheed Martin said in a Wednesday release that it now expects to deliver 97 F-35s, all in the previous TR-2 configuration. The company originally planned to deliver roughly 147 to 153 of the fighters this year.

Lockheed said it is continuing F-35 production, expecting to build 156 this year, while continuing to work on finalizing the development and testing of TR-3′s software.

The company also said it “remain[s] focused on receiving the necessary hardware from our suppliers to deliver this critical combat capability for the F-35,” identifying L3Harris Technologies’ work on the fighter’s Integrated Core Processor as contributing to the challenges.

“The development of the Integrated Core Processor by L3Harris has driven delays due to unexpected challenges associated with hardware and software development, component and system integration testing and system qualification testing,” Lockheed said. “The hardware development challenges impacted hardware/software integration, compressing the software testing schedule.”

Lockheed said it has sent its employees to L3Harris to speed up the hardware delivery, and is working with RTX to help with its delivery of the next-generation Electro-Optical Distributed Aperture System, another TR-3 component.

In a statement to Defense News, L3Harris disputed Lockheed’s claim that the Integrated Core Processor was part of the problem.

“L3Harris overcame some early design challenges and delivered a fully quantifiable Integrated Core Processor to Lockheed Martin well over a year ago,” L3Harris said. “In June ’22, L3Harris began delivering flight test hardware after completing safety of flight qualification testing. We continue to work closely with [Lockheed Martin] to support them in the integration of their software into the TR3 hardware.”

Defense News has also reached out to RTX for comment.

Lockheed’s prediction that 97 fighters would be delivered this year is also a lower estimate than the 100 to 120 fighters CEO Jim Taiclet offered in a July earnings call.

Tyndall Air Force Base in Florida recently received its first four F-35s as part of its effort to transition from its old training mission to a combat-capable F-35 fighter wing, according to Air Combat Command head Gen. Mark Kelly, while speaking in a panel at the Defense News Conference on Sept. 6 in Arlington, Virginia.

He added that other transitioning units, such as the Alabama Air National Guard’s 187th Fighter Wing, are still likely to get their first new F-35s on time.

Subsequent tranches of F-35s to complete those units’ complements could take a hit from the delay, Kelly said. The severity of the effect will depend on how long it is before F-35s start getting delivered again, he explained.

Kelly said the Air Force remains “in lockstep” with its industry partners on the F-35 and needs to help companies work through this challenge, which he called “way-hard business.”

The delays in a unit receiving new fighters will have a follow-on effect on the Air Force’s ability to manage itself worldwide, Kelly said.

“When a unit converts to a new airplane, usually by the time they get their last airplane, the clock starts and they need to be ready to go a year or so later,” Kelly noted. “That will delay and will impact … global force management.”

The Air Force will use its TR-2 F-35s until the newer configuration becomes available, he said. But in a fight against an advanced military able to employ serious electromagnetic threats, Kelly added, the Air Force must be able to employ the most up-to-date capabilities.

“If we’re going to engage those threats, we’ve got to have the fastest processing, the best jamming,” Kelly said. “That takes a really agile, stable software load to unlock this Block 4 hardware and unlock the EW [electronic warfare] that’s the secret sauce that we’re going to need.”

Lt. Gen. Jim Slife, deputy chief of staff for operations and the nominee to be the service’s next vice chief of staff, said that with the Air Force’s limited fighter capacity, it doesn’t have the ability to choose whether to send a TR-2 or TR-3 F-35 to an unfolding crisis.

“It’s a knife’s edge of capacity that we’re dealing with every day,” Slife said. “It’s frankly, check your pockets and see what you have in your pocket [when an emergency unfolds], and that’s what goes. Getting these jets on time and fielded is absolutely critical to our ability to meet the global demand signal on a day-to-day basis.”

Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.

More In Air Warfare