Correction: A previous version of this story misinterpreted a BAE Systems statement.

FORT WORTH, Texas — On a mile-long production line in Fort Worth, Texas, the next wave of the U.S. and allied militaries’ F-35 Joint Strike Fighter fleets takes shape.

Dozens of nascent fighters, coated almost entirely in sea-green primer, work their way north through Air Force Plant 4, a government-owned facility operated by manufacturer Lockheed Martin. They begin their journey here as a pair of wings hanging from blue platforms on the southern end. Along the way, Lockheed employees — the entire site has about 17,000 workers — add the engines, cannons, tails, rudders, lift fans, canopies, landing gear, sensors and other components that make the Lightning II the most advanced fighter jet ever made.

Plant 4 is also where Lockheed Martin has faced significant challenges, from labor and supply chain shortages spurred by the COVID-19 pandemic to the recent discovery that a key magnet in a subcontractor’s part had for years been made with an unauthorized China-sourced alloy.

In an interview with Defense News during a Nov. 2 visit to the plant, Edward Smith, Lockheed’s director of F-35 domestic engagement, said the company is on track to start delivering the first Lot 15 fighters in late 2023, and it’s a few years away from making up the production losses caused by the pandemic.

Recent economic turmoil complicated and prolonged the contract negotiating process for lots 15 through 17, but Lockheed expects to sign a final agreement by the end of the year.

“Think about what was happening when we were finalizing the [2021] budget [proposal] — it was pre-COVID,” Smith said. “Since then, we’ve gone through a worldwide shutdown of the supply chain. … We’ve seen inflation that we haven’t seen since the ’70s. … We had suppliers that are so uncertain about their supply chain that some of them were unwilling to predict out further than six months on what their costs were going to be.”

Now, several years of declining per-unit prices — the cost of an F-35A steadily decreased from $89 million in Lot 11 to nearly $78 million by Lot 14 — are about to come to an end. The lower quantity of purchased fighters, the pandemic and the addition of more capabilities will cause the price of an F-35 to rise in the coming lots, Smith said.

“You’re adding capabilities, you’re buying more of a jet now,” he explained. “Your prices are going to go up a bit. You can’t [get the price lower] by cutting 100 airplanes out of a lot buy.”

From Liberator to Lightning II

The walls of Air Force Plant 4 have seen decades of history. It began operating 80 years ago under Consolidated Aircraft, a Lockheed predecessor, turning out B-24 Liberator and B-32 Dominator bombers to fight in World War II. Over the years, other aircraft produced here have included the sweep-wing F-111 Aardvark, the F-16 Fighting Falcon and parts of the F-22A Raptor.

Scenes from the James Stewart movie “Strategic Air Command” were filmed on the flight line. And the Texas Historical Commission in 2008 designated the site a historical landmark for its role in World War II. This limits how much Lockheed Martin can modify the plant’s structure, though the company has learned to adapt.

Today, this is Lockheed’s primary site for producing the F-35 — the only facility that turns out all three variants of the fifth-generation fighter, over three shifts operating around the clock, usually five days a week. A handful of F-35s are also built in Italy and Japan. The fighters built at Forth Worth will eventually go to U.S. Air Force, Navy and Marine Corps units, as well as allies such as the U.K., Denmark, Norway, Belgium and Israel.

The entire site totals 1 mile and 25 feet, and it covers 7.5 million square feet — about the size of 130 football fields. About 4,000 employees work in the main construction facility, with the remainder in other areas.

Dozens of wings hang in pairs — as many as 33 pairs — on the southern end of Plant 4, where they are joined to a center structure. They are then mated to other fuselage sections made by Northrop Grumman and BAE Systems before moving onto the final assembly area, where components both large and small are added and fastened into place.

When an F-35 is finished, its nose gear is hooked to a tow bot that wheels the aircraft through the front of the facility, where it is taken to another building to test structural durability. Then, the F-35 is moved to another humidity-controlled final finishing facility where twin robots dubbed Zeus and Thor apply stealth coating.

That’s how the process usually works. But when the coronavirus pandemic hit in early 2020, it forced Lockheed Martin to make several adjustments on the fly.

COVID and other curveballs

Lockheed began changing its F-35 production line operations during the first few months of the pandemic, moving to shore up its supply chains and adjust work schedules.

COVID-19 quickly took a bite out of the F-35′s production schedule — an area where Lockheed is still playing catch-up. The company originally planned to deliver 141 fighters in 2020, but realized that spring it simply wasn’t going to happen. The contractor eventually produced 120 that year.

Because much of Lockheed’s F-35 supply chain is sourced in the U.S., Smith said, it was largely able to avoid the worst of the crunches that affected other parts of the defense industry, such as shipping bottlenecks at backed-up ports.

But Lockheed wasn’t entirely immune. For example, BAE Systems builds the F-35′s aft fuselage in Lancashire, England. The U.K. had stricter COVID-19 lockdowns than America, which hindered production, Smith said.

“One of the biggest supplier effects was labor,” he explained. “People just weren’t allowed to go to work, for some of our suppliers.”

In a statement to Defense News, BAE Systems said its F-35 production work in the U.K. resumed in April 2020 after a temporary pause.

A slowdown in F-35 construction was inevitable, according to Smith. But it wouldn’t last forever, and the company didn’t want to lay off skilled, experienced employees it would need when work picked back up.

“With that backlog [from the U.K.], we saw it coming,” Smith said. The company realized “they’re going to start back, but there’s going to be a gap because everybody shut down for a while. So how do we [manage the slowdown]? You don’t take a workforce of 17,000 employees and tell them to go home.”

Lockheed decided to “stretch the work we have,” Smith said. The company sat down with its employees’ union, the International Association of Machinists and Aerospace Workers District Lodge 776, and they hashed out an adjusted work schedule — one that would allow F-35 construction to continue, while allowing for easier social distancing during the pre-vaccine months of the pandemic.

From May to early September 2020, Lockheed Martin divided each of its F-35 shifts at Fort Worth into three groups, which then worked on a two-weeks-on, one-week-off schedule.

By the end of the summer, Smith said, BAE had worked through its supply issues, and normal work could resume at Fort Worth without any layoffs or loss of pay or benefits. A union spokesman told Defense News its members too saw the alternate schedule as a success.

Absenteeism during the pandemic was unavoidable, Smith said. At its peak in February 2021, the absentee rate almost doubled compared to pre-pandemic levels. But a year later, it had largely subsided. From January 2021 to April 2022, Lockheed added about 700 employees to the line to make up for absences and ensure it could meet demand, the company told Defense News.

Lockheed also took steps to keep its suppliers — particularly smaller firms — operating during the tumultuous period, Smith said. “There’s a lot of mom and pop shops out there that, if contracts stop coming, they’ve got about three months, and then they’re out of business.”

Lockheed adopted a so-called forward-funding strategy of paying them three or four months early. In March 2020, the Pentagon upped progress payment rates to large businesses like Lockheed from 80% to 90%. Lockheed said it in turn forwarded those payments to its own supply chain. In 2021, the contractor said it averaged about $400 million in accelerated payments each week to its suppliers, particularly small and vulnerable businesses.

Smith said this allowed Lockheed’s smaller subcontractors to buy long-lead parts — items that take a long time to produce or deliver — knowing there would be business waiting when the parts arrived.

In early 2021, Lockheed also began striking long-term agreements with suppliers, which Smith said helped mitigate some of the effects of inflation.

Lockheed spokeswoman Laura Siebert said finding savings in the supply chain process will be key to keeping costs down for lots 15 through 17, which will produce about 375 F-35s. That’s about 100 fewer than the 2019 deal for the previous three lots.

“With the lower [production] numbers, we were still able to beat inflation metrics [in the] cost,” she said. “You’ll see that in 15 through 17. And a lot of it has to do with supply chain [savings].”

Lockheed was able to cut per-tail costs to about $78 million for Lot 14. From now on, Smith said, the cost of each F-35 is likely to increase because of inflation, lower quantities and added capabilities. Lot 15 jets are to be the first to come with Technology Refresh 3 already installed — a series of upgrades to the F-35′s hardware and software meant to improve its displays, processing capability and memory.

Smith said these improvements will allow the fighter to store and process more data as well as provide the “backbone” for the upgrades that will make up the F-35′s Block 4 modernization effort.

Block 4 will include the ability to carry more weapons, better recognize targets and conduct advanced electronic warfare. Smith said the F-35 is on track for 75 major upgrades that will introduce about 518 capabilities, without changing its outer skin.

After the worst of the pandemic’s crunch passed, Lockheed ramped up its production. By 2025, the company expects to be back on schedule.

Last year, the contractor delivered 142 fighters, beating the upper end of its yearly goal by three. In 2022, the company is on track to produce 148 to 153 F-35s. In 2023, Smith said, the production rate will probably be about the same as this year as the company works to overcome lingering supply chain issues. Some of those problems are related to the war in Ukraine, which has affected European raw material suppliers.

“Supply chain problems are going to cascade for the next several years,” according to Smith.

In subsequent years, he added, “our intent is to continue to ramp” up production. In a re-baseline agreement for the F-35 program struck in September 2021, Lockheed agreed to start delivering 156 F-35s a year from 2023, onward.

Right now, Lockheed is wrapping up production of Lot 13 F-35s, and the company expects to deliver much of the remaining Lot 14 fighters in the first half of 2023.

The firm is already starting production of Lot 15 at the Fort Worth factory, and deliveries are expected to begin in the second half of 2023.

Lot 16 and 17 fighters will follow, and Smith said some sub-suppliers are already starting preliminary work on some parts that will go into Lot 16.

‘A wrestling match’

Once construction ends, completed F-35s prepare for their first flight by Lockheed Martin test pilots. For the F-35B, the short-takeoff-and-vertical-landing variant flown by the U.S. Marine Corps, test pilots also take the fighters up for a short hover.

Four or five fighters are flown each day on average, sometimes more, said test pilot Brian “Banski” Bann, who flew Harriers for the Marine Corps. But clear skies are a must for these acceptance flights, Bann noted, so they don’t fly when it’s cloudy.

At first, the test pilots take an F-35 up to about 15,000 feet for a relatively shorter flight to check its engine, Bann said. At that height, he added, if the engine malfunctions, it’s still possible to glide back down.

And then the test pilots can really take the F-35 for a spin: a supersonic flight test at 35,000-40,000 feet that can last 1 hour and 45 minutes, pushing pilots to their G-force limits and leaving them drenched in sweat.

“It’s like being in a wrestling match,” Bann said.

At the north end of Plant 4, a newly assembled F-35A waited just inside the open hangar doors as about a half-dozen employees gathered around.

This fighter will soon be the Air Force’s 361st F-35A. It’s destined for RAF Lakenheath in England, where the service is setting up its first permanent F-35 squadrons in Europe. In years and decades to come, it will likely be flown on patrols in and around Europe, perhaps engaging in combat.

But on this day, some employees slowly walked around the aircraft, scanning the ground for rocks or other debris that could damage the fighter.

A younger worker cautiously guided the tow bot wheeling the F-35A, pulling the fighter into the sunlight for the first time. It was this employee’s first time controlling the robot, and when he was done, his colleagues gave him a smattering of applause.

“He did good,” a manager said.

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 He has traveled to the Middle East to cover U.S. Air Force operations.