The Defense Department is paying an additional $5.57 billion to expand the U.S. military’s arsenal of F-35 Joint Strike Fighters by 74. (Christophe Archambault/AFP/Getty Images)

The Defense Department has announced that it is paying $5.57 billion to expand the U.S. military’s arsenal of F-35 Joint Strike Fighters by 74 planes.

The contract action is seen as an early stamp of progress for the next “lot” of planes, which the Defense Department Joint Program Office and Bethesda-based defense manufacturer Lockheed Martin are negotiating. Joint Program Office spokesman Joe DellaVedova said that the round of planes is set to include 50 planes sold to foreign governments, bringing the total to 141 planes in this sales lot.

“We appreciate the actions taken by the JPO to ensure delivery of F-35s to our warfighter customers,” Lockheed Martin said in a statement.

What remains to be determined is the unit cost of the plane. Price disputes have derailed the program in the past, such as when the F-35 Joint Program Office unilaterally imposed its own pricing for the ninth lot of planes after more than a year of negotiations.

The F-35 Joint Strike Fighter is designed to be the next-generation fighter jet that will replace the F-16 as the most advanced air asset of the United States and its allies. It can take off and land vertically and can carry munitions inside the body of the plane. Its $400,000-a-pop helmet has an augmented reality display that gives the pilot a view through the bottom of the plane.

It is also the single most expensive military program in the history of the Pentagon, accounting for about a quarter of Lockheed Martin’s annual revenue and considered critical to its status as a top-tier defense contractor. A spate of program delays and ballooning development costs have made “the plane that ate the Pentagon” into something of a poster child for bureaucratic waste, drawing criticism from Republicans and Democrats alike.

Then President-elect Donald Trump joined that debate before he was sworn into office, suggesting in a tweet that the plane should be replaced with Boeing’s cheaper F-18 Super Hornet. The Pentagon subsequently ordered a review to weigh the two planes’ competing advantages.

The Pentagon and Lockheed Martin subsequently agreed to sell the 10th lot of 90 planes at about $85 million per plane, a price that was roughly in line with what the Pentagon had planned before Trump took office. A Joint Program Office statement said the unit price for lot 11 is expected to be less than that.

Advocates of the program described the new contract order as a sign that the program is moving past its history of delays and false starts. Industry experts have generally credited the Trump administration with speeding along negotiations.

“The program certainly seems to be moving faster than it did during the Obama years,” said Loren Thompson, a defense consultant with the Lexington Institute, which receives funding from defense firms, including Lockheed Martin.