In a ceremony in June at Joint Base Myer-Henderson Hall in Arlington, Va., four current and former executives from Meta, OpenAI and Palantir lined up onstage to swear an oath to support and defend the United States.

The U.S. Army had just created a technical innovation unit for the executives, who were dressed in combat gear and boots. At the event, they were pronounced lieutenant colonels in the new unit, Detachment 201, which will advise the Army on new technologies for potential combat.

“We desperately need what they are good at,” Secretary of the Army Daniel Driscoll said of the tech executives, who have since undergone basic training. “It’s an understatement how grateful we are that they are taking this risk to come and try to build this out with us.”

The military is not just courting Silicon Valley tech companies. In the age of President Trump, it has successfully recruited them.

Over the past two years, Silicon Valley’s leaders and investors — many of whom had once forsworn involvement in weapons and war — have plunged headfirst into the military industrial complex. Meta, Google and OpenAI, which once had language in their corporate policies banning the use of artificial intelligence in weapons, have removed such wording. OpenAI is creating anti-drone technology, while Meta is making virtual reality glasses to train soldiers for battle.

At the same time, weapons and defense start-ups are taking off. Andreessen Horowitz, a venture capital firm, said in 2023 that it would invest $500 million in defense technology and other companies that would help America “move forward.” Y Combinator, the start-up incubator known for hatching companies like Airbnb and DoorDash, funded its first defense start-up in August 2024. Venture capital investment in defense-related companies surged 33 percent last year to $31 billion, according to McKinsey.

The change is part of a major cultural shift in Silicon Valley. A decade ago, tech companies brandished mottos such as “connecting the world” and “do no evil” and pledged that their technology would not be used for military purposes. Working with the U.S. government was so unpopular that software and cloud computing contracts with the Department of Defense fueled tech employee protests.

Now “the tides have turned,” Andrew Bosworth, Meta’s chief technology officer and one of the new lieutenant colonels in Detachment 201, said at a tech conference in San Francisco in June. “There’s a much stronger patriotic underpinning than I think people give Silicon Valley credit for.” He is set to serve some reserve duty days with the Army each year.

The militarization of the nation’s technology capital has been driven by a changing political climate, competition with China for tech leadership and the wars in Ukraine and Gaza, where drones and A.I.-backed weapons systems have become crucial in battles. Those wars pushed the Pentagon to begin modernizing America’s weapons arsenal, a move that Mr. Trump has supported.

In April, Mr. Trump issued an executive order calling for the military to update the system it uses to acquire new technology. His domestic policy bill allocated a record $1 trillion to defense in 2026, including for technology such as autonomous drones. Silicon Valley executives and venture capitalists are eagerly eying that bonanza.

“Protecting democracies is important,” said Raj Shah, a managing partner at Shield Capital, a venture capital firm in San Francisco that invests in defense and security technology. “You have bad authoritarians out there who don’t believe in borders.”

But some tech executives and engineers are wrestling with the potential harms of the shift. Once they build autonomous drones and A.I. weapons for the military, they will have little control over how the technology is deployed. That has led to debates over whether more people will be killed by these advanced weapons than traditional ones, three engineers at Google and Meta said.

“These Silicon Valley companies are hyper competitive, and in their drive to get into these defense sectors, there isn’t a lot of pausing to think,” said Margaret O’Mara, a tech historian at the University of Washington.

Rooted in Defense

Silicon Valley’s militarization is in many ways a return to the region’s roots.

Before the area was a tech epicenter, it was a bucolic land of fruit orchards. In the 1950s, the Defense Department began investing in tech companies in the region, aiming to compete with Russia’s technological advantages in the Cold War. That made the federal government the first major backer of Silicon Valley.

The Defense Advanced Research Projects Agency, a division of the Department of Defense, later incubated technology — such as the internet — that became the basis for Silicon Valley’s largest companies. In 1998, the Stanford graduate students Sergey Brin and Larry Page received funding from Darpa and other government agencies to create Google.

But in the late 1990s and 2000s, tech companies turned toward consumer technology such as e-commerce and social networks. They presented themselves as doing good and democratizing technology for the masses, drawing a largely liberal work force that was opposed to working with the defense establishment.

In 2018, more than 4,000 Google employees protested a Pentagon contract called Project Maven, which would have used the company’s A.I. to analyze drone surveillance footage. In a letter to executives, the employees said Google “should not be in the business of war.”

Google soon said it would not renew the Pentagon contract and dropped out of a race for a $10 billion cloud computing contract called JEDI for the Department of Defense.

That year, Google published guiding principles for future A.I. projects, forbidding A.I. for “weapons or other technologies whose principal purpose or implementation is to cause or directly facilitate injury to people.” Other companies followed with similar pledges.

There were outliers. Alex Karp, the chief executive of Palantir, a tech data analytics firm founded in 2003, was so enthusiastic for Silicon Valley to take a bigger role in defense that he sued the Army in 2016 to force it to consider buying Palantir’s software. Palantir claimed the Army was failing to look at commercial options for its needs.

Palantir won the suit. Other tech companies provided the Defense Department with software and cloud computing, among other services.

In 2015, Defense Secretary Ashton Carter visited Silicon Valley to open the Defense Innovation Unit, a flagship military program to speed the adoption of advanced technology. But start-ups said the bureaucratic process for signing deals with the Pentagon made the program untenable.

“We weren’t as agile as the people we wanted to connect to want to be,” Mr. Carter acknowledged at a 2016 tech conference.

Proud to Engage

After the wars in Ukraine and Gaza brought autonomous drones and facial recognition software to battlefields, Silicon Valley engineers and executives said they realized it was no longer theoretical that the next war would be won by the military with the most advanced technologies.

The political climate also shifted, with some executives and venture capitalists openly supporting right-wing views and candidates. Competition with China over technological superiority led many techies to lean more toward the U.S. government as an ally.

Palantir became a model for other tech companies. With contracts across the U.S. government and military for software that organizes and analyzes data, the company’s market value ballooned to more than $375 billion this month, more than the combined market capitalization of traditional defense contractors like Lockheed Martin, Northrop Grumman and General Dynamics.

In a shareholder letter in May, Mr. Karp said critics once dismissed Palantir’s interest in “arming the United States of America” but that “some within the Valley have now turned a corner and begun following our lead.”

Palantir did not respond to a request for comment.

Other Silicon Valley companies also turned toward defense. In January 2024, OpenAI, the maker of the ChatGPT chatbot, deleted language in its policy page that prohibited the use of its technology for “weapons development” and “military and warfare.” That December, the company announced a deal with Anduril, a defense technology start-up, to build anti-drone A.I. systems.

Asked for comment, an OpenAI spokeswoman pointed to an April conversation between Sam Altman, the company’s chief executive, and Gen. Paul M. Nakasone, an OpenAI board member and former head of the National Security Agency.

“We have to, and are proud to, and really want to engage in national security areas,” Mr. Altman said, adding that OpenAI would help develop A.I. when it was “supporting the U.S. and our allies to uphold democratic values around the world and to keep us safe.”

(The New York Times has sued OpenAI and its partner, Microsoft, over copyright infringement of news content. Both companies have denied wrongdoing.)

Last year, Meta changed its policies to allow its A.I. technologies to be used for military purposes. In May, the company announced a partnership with Anduril to develop virtual reality devices to train soldiers. At the time, Mr. Bosworth said America’s “national security benefits enormously from American industry bringing these technologies to life.”

In February, Google announced it, too, was discarding its self-imposed ban on using A.I. in weapons. In a blog post, the company said there was “a global competition taking place for A.I. leadership within an increasingly complex geopolitical landscape. We believe democracies should lead in A.I. development.”

Google and Meta declined to comment.

One beneficiary of the shift is Anduril, which was founded in 2017 by Palmer Luckey, a tech entrepreneur who developed the Oculus virtual reality headset. Anduril, which designs A.I.-backed weapons, signed a $642 million contract for anti-drone technology with the Marine Corps in March, and a $250 million contract to advance air defense technology for the Department of Defense in October.

In June, Anduril announced it had raised $2.5 billion in new funding at a $30.5 billion valuation. The company declined to comment.

The embrace of defense was punctuated by the four tech executives enlisting in the new army unit in June. They were Meta’s Mr. Bosworth, Palantir chief technology officer Shyam Sankar, OpenAI chief product officer Kevin Weil and Bob McGrew, an adviser at Thinking Machines Lab and OpenAI’s former chief research officer. The army had called Mr. Sankar about the unit and he recommended the other executives, an army spokesman said.

‘A Hype Cycle’

When Billy Thalheimer attended a session at the Silicon Valley start-up incubator Y Combinator in 2021, he saw himself as the misfit.

As chief executive of Regent, a company that builds electric seagliders for military and other purposes, he said he noticed “a real stigma against defense tech.” Other start-ups at Y Combinator hawked crypto projects, Mr. Thalheimer recalls.

Now there are hundreds of start-ups focused on defense technology, he said. “It’s clear we are in a hype cycle,” he said.

Since 2023, Regent has raised more than $100 million from investors including Mark Cuban and Peter Thiel. In March, the company landed a $15 million contract with the Marine Corps and is building a factory in Rhode Island.

In Hayward, Calif., production has ramped up at the factory of Skydio, an autonomous drone company. In June, the start-up signed a $74 million contract with the State Department to provide drones for global counternarcotics and law enforcement.

Adam Bry, who founded Skydio in 2014, said there has been a huge shift in how quickly the military is filling a need for new technology. It took three years to sign his first contract to supply drones to the army, but a new contract this year to continue supplying drones to the army took less than a month.

“For the first time, we’re seeing a real sense of urgency,” Mr. Bry said. Skydio, which has raised $230 million, has more than 800 employees.

Silicon Valley’s closer relationship with the defense establishment was evident in March, when hundreds gathered in Washington for a summit hosted by Andreessen Horowitz. The venture capital firm highlighted its “American Dynamism” program, which includes investing in defense companies.

“Investing in defense technology is both necessary and urgent,” David Ulevitch, a general partner at Andreessen Horowitz, said in a statement. “Technological superiority is a requirement for a strong democracy.”

The featured speaker was Vice President JD Vance, a former venture capitalist who once invested in Anduril.

“We shouldn’t be fearful of productive new technologies, in fact we should seek to dominate them,” Mr. Vance said. “That is certainly what this administration wants to accomplish.”