On Air Force fighter jets, magnets made of rare earth minerals that are mined or processed in China are needed to start the engines and provide emergency power.
On precision-guided ballistic missiles favored by the Army, magnets containing Chinese rare earth materials rotate the tail fins that allow missiles to home in on small or moving targets. And on new electric and battery-powered drones being adapted by Marines, rare earth magnets are irreplaceable in the compact electric motors.
China’s decision to retaliate against President Trump’s sharp increase in tariffs by ordering restrictions on the exports of a wide range of critical minerals and magnets is a warning shot across the bow of American national security, industry and defense experts said.
In announcing that it will now require special export licenses for six heavy rare earth metals, which are refined entirely in China, as well as rare earth magnets, 90 percent of which are produced in China, Beijing has reminded the Pentagon — if, indeed, it needed reminding — that a wide swath of American weaponry is dependent on China.
“This decision is hugely consequential for our national security,” said Gracelin Baskaran, director of the Critical Minerals Security Program with the Center for Strategic and International Studies.
Beijing, by beginning with what one Air Force official called a “heads-up” shot meant to signal how much more harm it could inflict should it choose, has left itself plenty of room to escalate. Beijing could also move on from the licensing restrictions to impose tariffs, quotas or even an all-out ban.
Rare earths are a group of 17 elements, including neodymium, yttrium, scandium and dysprosium, that are difficult to separate into usable forms. They are not actually rare at all but can be difficult to extract from the earth, and the process of mining and refining them into usable form carries substantial environmental costs.
They are present in almost every form of American defense technology. They can form very powerful magnets, for use in fighter jets, warships, missiles, tanks and lasers. Yttrium is required for high-temperature jet engine coatings; it allows thermal barrier coatings on turbine blades to stop aircraft engines from melting midflight.
According to the Defense Department, every F-35 fighter contains around 900 pounds of rare earth materials. Some submarines need more than 9,200 pounds of the materials.
Across the American defense industry, aerospace and weapons companies have small stockpiles of the rare earths — the industry term for the 17 elements. That is enough, defense industry analysts say, to meet their needs for months rather than years.
The Pentagon also has stockpiles of some rare earths, but those reserves are not enough to sustain defense companies indefinitely, one official said.
“China mines and refines most of the world’s rare earths, and dominates the downstream supply chain,” said Aaron Jerome, a trader at Lipmann Walton and Co., a metals trading company based in Britain. That supply-chain dominance allows Beijing some say over just how much weaponry that is dependent on the rare earths will cost, giving it enormous power over America’s defense industrial base.
Mr. Jerome pointed to what he called “the F-35 magnet debacle.” Back in 2022, the Pentagon temporarily stopped deliveries of Lockheed Martin’s F-35 after the manufacturer acknowledged that an alloy made in China was in a component of the stealth fighter jet, violating federal defense acquisition rules.
At the time, the Pentagon said a magnet containing the alloy used in part of the integrated power package posed no security problem.
But just one month later, the Pentagon allowed the deliveries to continue while it looked for another source for the magnets. Wherever the magnets are coming from now, some component of it is controlled by Beijing’s lock on the supply chain, Mr. Jerome said.
With Beijing now requiring that its exporters of rare earths first receive express permission from the government before sending the material to the United States, American defense companies may see prices shoot up soon, industry experts said.
As recently as the 1980s, the United States was a leader in rare earth production, through the Mountain Pass mine in California. But by 2002, Mountain Pass had shut down, with China dominating the market. Mountain Pass is now owned by MP Materials and is operating again, but it does not come close to Chinese production, industry experts said.
The Aerospace Industries Association, representing defense contractors, two years ago called again for the United States to shore up its minerals supply chain to better secure access for the industry.
“U.S. global leadership in aerospace and defense hinges on a secure and resilient supply chain — particularly for the critical minerals used in the production of cutting-edge aircraft technology,” Eric Fanning, the organization’s president, said at the time.
China has flexed its muscle over the rare earth supply chain in the past. In 2010, Beijing halted rare earths trade with Japan following Japan’s detention of a Chinese fishing trawler captain. The Chinese move caught the attention of the United States, alerting it to the threat posed by China’s control over the minerals’ supply chain.
In 2017, during his first term, Mr. Trump signed an executive order aimed at boosting U.S. domestic production, and President Joseph R. Biden Jr. followed suit during his administration, allocating even more money for rare earth extraction and refinement facilities.
The Pentagon has been adding to its stockpile since the 2010 episode involving Japan, and “we have more of a stockpile than we did 15 years ago,” said Dan Blumenthal, senior fellow at the American Enterprise Institute. But, he added, “that will not last long enough.” American defense companies, he said, “should be very worried.”
There is historical precedent for the United States’ finding alternatives to crucial elements and minerals during wartime. In World War II, German U-boats sank many Allied cargo ships carrying bauxite from Suriname. “We would potentially have lost the war if we did not get alternative sources for bauxite,” said Seth G. Jones, author of the upcoming book “The American Edge: The Military Tech Nexus and the Sources of Great Power Dominance.”
The United States turned to Arkansas and built a large stockpile of bauxite, used to build airplanes, from mines there.