Bailey Baumbick knew she wanted to serve her country when she graduated from Notre Dame in 2021. Ms. Baumbick, a 26-year-old from Novi, Mich., didn’t enlist in the military, however. She enrolled in business school at the University of California, Berkeley.

Ms. Baumbick is part of a growing community in the Bay Area that aims to bring high-tech dynamism to the lumbering world of the military. After social media companies and countless lifestyle start-ups lost their luster in recent years, entrepreneurs are being drawn to defense tech by a mix of motivations: an influx of venture capital, a coolness factor and the start-up ethos, which Ms. Baumbick describes as “the relentless pursuit of building things.”

There’s also something deeper: old-fashioned patriotism, matched with a career that serves a greater purpose.

In college Ms. Baumbick watched her father, a Ford Motor Company executive, lead the company’s sprint to produce Covid-19 ventilators and personal protective equipment for front-line health care workers. “I’ve never been more inspired by how private sector industry can have so much impact for public sector good,” she said.

Ford’s interventions during the Covid-19 pandemic hark back to a time when public-private partnerships were commonplace. During World War II, leaders of America’s biggest companies, including Ford, halted business as usual to manufacture weapons for the war effort.

For much of the 20th century, the private and public sectors were tightly woven together. In 1980, nearly one in five Americans were veterans. By 2022, that figure had shrunk to one in 16. Through the 1980s, about 70 percent of the companies doing business with the Pentagon were also leaders in the broader U.S. economy. That’s down to less than 10 percent today. The shift away from widespread American participation in national security has left the Department of Defense isolated from two of the country’s great assets: its entrepreneurial spirit and technological expertise.

Recent changes in Silicon Valley are bringing down those walls. Venture capital is pouring money into defense tech; annual investment is up from $7 billion in 2015 to some $80 billion in 2025. The Pentagon needs to seize this opportunity, and find ways to accelerate its work with start-ups and skilled workers from the private sector. It should expand the definition of what it means to serve and provide more flexible options to those willing to step in.

The military will always need physically fit service members. But we are headed toward a future where software will play a bigger role in armed conflict than hardware, from unmanned drones and A.I.-driven targeting to highly engineered cyber weapons and space-based systems. These missions will be carried out by service members in temperature-controlled rooms rather than well armed troops braving the physical challenges of the front line.

For all the latent opportunity in Silicon Valley and beyond, the Trump administration has been uneven in embracing the moment. Stephen Feinberg, the deputy secretary of defense, is a Wall Street billionaire who is expanding the Pentagon’s ties with businesses. Pete Hegseth, the secretary of defense, his “warrior ethos” and exclusionary recruitment have set back the effort to build a military for the future of war.

America has the chance to reshape our armed forces for the conflicts ahead, and we have the rare good fortune of being able to do that in peacetime.

Elias Rosenfeld had been at Stanford for only a month and a half, but he already looked right at home at a recent job fair for students interested in pursuing defense tech, standing in a relaxed posture, wearing beaded bracelets and a sweater adorned with a single sunflower. Rather than use his time in Stanford’s prestigious business school to build a fintech app or wellness brand, Mr. Rosenfeld has set his sights on helping to rebuild the industrial base on which America’s military relies.

It’s a crucial mission for a country that is getting outbuilt by China, and Mr. Rosenfeld brings a unique commitment to it. Born in Venezuela, he came to the United States at age 6 and draws his patriotism from that country’s experience with tyranny and his Jewish heritage. “Without a strong, resilient America, I might not be here today,” Mr. Rosenfeld says. Working on industrial renewal, he says, is a way to “start delivering as a country so folks feel more inclined and passionate to be more patriotic.”

Not on Mr. Rosenfeld’s agenda: enlisting in the military. In an earlier era, he might have been tempted by a wider suite of options for service. In 1955 the U.S. government nearly doubled the maximum size of the military’s ready reserve forces, from 1.5 million to 2.9 million, in part by giving young men the chance to spend six months in active duty training. Today the U.S. ready reserve numbers just over a million.

Other countries provide a model for strengthening the reserves. In Sweden, the military selects the top 5 percent or so of 18-year-olds eligible to serve in the active military for up to 15 months, followed by membership in the reserve for 10 years. The model is so effective that recruits compete for spots, and according to The Wall Street Journal, “former conscripts are headhunted by the civil service and prized by tech companies.”

America’s leaders have argued for a generation that the military’s volunteer model is superior to conscription in delivering a well-prepared force. The challenge is maintaining recruiting and getting the right service members for every mission. There are some examples of the Pentagon successfully luring new, tech-savvy recruits. Since last year, top college students have been training to meet the government’s growing need for skilled cybersecurity professionals. The Cyber Service Academy, a scholarship-for-service program, covers the full cost of tuition and educational expenses in exchange for a period of civilian employment within the Defense Department upon graduation. Scholars work in full-time, cyber-related positions.

The best incentive for enlisting may have nothing to do with service, but the career opportunities that are promised after.

It was a foregone conclusion that Lee Kantowski would become an Army officer. One of his favorite high school teachers had served, and his hometown, Lawton, Okla., was a military town, a place where enlisting was commonplace. Mr. Kantowski attended West Point and, in the eight years after graduating, went on tours across the world. Now he’s getting an M.B.A. at U.C. Berkeley, co-founded a defense tech club with Ms. Baumbick there and works part-time at a start-up building guidance devices that turn dumb bombs into smart ones.

The military needs recruits like Mr. Kantowski who want to support defense in and out of uniform. Already, nearly one million people who work for the Department of Defense are civilians, supplemented by a similar number of contractors who straddle public and private sectors. Both paths could be expanded.

A rotating-door approach carries some risk to military cohesion and readiness. The armed services are not just another job: Soldiers are asked to put themselves in danger’s way, even outside combat zones. America still needs men and women who are willing to sign up for traditional tours of duty.

The Reserve Officers’ Training Corps serves as the largest source of commissioned officers for the U.S. military. For more than five decades, R.O.T.C. has paid for students to pursue degree programs — accompanied by military drills and exercises — and then complete three to 10 years of required service after graduation. In 1960 alone, Stanford and M.I.T. each graduated about 100 R.O.T.C. members. Today, that figure is less than 20 combined. The Army has recently closed or reorganized programs at 84 campuses and may cut funding over the next decade.

This is exactly the wrong call. R.O.T.C. programs should be strengthened and expanded, not closed or merged.

It remains true that the volunteer force has become a jobs program for many Americans looking for a ladder to prosperity. It’s an aspect of service often more compelling to enlistees than the desire to fight for their country. In the era of artificial intelligence and expected job displacement, enlistment could easily grow.

Most military benefits have never been more appealing, with signing and retention bonuses, tax-free housing and food allowances, subsidized mortgages, low-cost health care, universal pre-K, tuition assistance and pensions. The Department of Defense and Congress need to find ways to bolster these benefits and their delivery, where service members often find gaps.

Standardizing post-service counseling and mentorship could help. Expanding job training programs like Skillbridge, which pairs transitioning service members with private sector internships, could also improve job prospects. JPMorgan has hired some 20,000 veterans across the country since creating an Office of Military & Veterans Affairs in 2011; it has also helped create a coalition of 300 companies dedicated to hiring vets.

When veterans land in promising companies — or start their own — it’s not just good for them. It’s also good for America. Rylan Hamilton and Austin Gray, two Navy veterans, started Blue Water Autonomy last year with the goal of building long-range drone ships that could help the military expand its maritime presence without the costs, risks and labor demands of deploying American sailors.

Mr. Gray, a former naval intelligence officer who worked in a drone factory in Ukraine, said Blue Water’s vessels will one day do everything from ferrying cargo to carrying out intelligence, surveillance and reconnaissance missions. This summer, the company raised $50 million to construct a fully autonomous ship stretching 150 feet long.

Before dawn on a Wednesday morning in October, military packs filled with supplies and American flags sat piled on a dewy field near the edge of Stanford University’s campus. Some of the over 900 attendees at a conference on defense tech gathered around an active-duty soldier studying at the school. The glare of his head lamp broke through the darkness as he rallied the group of students, founders, veterans and investors for a “sweat equity” workout.

“Somewhere, a platoon worked out at 0630 to start their day,” he said. “This conference is all about supporting folks like them, so we are going to start our day the same way.” The group set off for Memorial Church at the center of campus, sharing the load of heavy packs, flags and equipment along the way.

That attitude is a big change for the Bay Area, not just from the days of 1960s hippie sit-ins but also from the early days of the tech revolution, when Silicon Valley was seen as a bastion of government-wary coders and peaceniks. Now it’s open for business with the Defense Department. “The excitement is there, the concern is there, the passion is there and the knowledge is there,” says Ms. Baumbick.

There are some risks to tying America’s military more closely to the tech-heavy private sector. Companies don’t always act in the country’s national interest. Elon Musk infamously limited the Ukrainian military’s access to its Starlink satellites, preventing them being used to help in a battle with Russian forces in 2022. Private companies are also easier for adversaries to penetrate and influence than the government.

Yet in order to prevent wars, or win them, we must learn to manage the risks of overlap between civilian and military spheres. The private sector’s newly rekindled interest in the world of defense is a generational chance to build the military that Americans need.