Clad in her signature red hat and coat, clenched fist raised high, Jane Fonda saluted the sea of chanting people who had gathered for her final “Fire Drill Friday” this week. She cheered as 147 of them were arrested on the steps of the Capitol building. And then she marched down Pennsylvania Avenue to the Chase Bank branch at the junction of Seventh Street SE where environmentalist Bill McKibben and about two dozen fellow activists had staked out in protest of the bank’s financing of oil and gas companies.

“Move your money, Chase, or we’ll move ours,” the outside demonstrators shouted, as Metropolitan Police filed into the bank to apprehend McKibben and nine others. “Fossil fuels have got to go!”

It was a climactic end to the two-time Academy Award winner and longtime activist’s weekly protest in Washington. But it was also the start, organizers said, of broader movement and a more aggressive push against financial institutions’ ties to the fossil fuel industry.

Since October, each Fire Drill Friday installment has featured a rotating cast of experts, activists and Fonda’s celebrity friends giving speeches on environmental issues. And each one has ended the same way: with Capitol Police strapping zip ties around participants’ wrists and charging them with obstruction.

But, fueled by the power of Fonda’s celebrity and a growing sense of urgency about the warming planet, the campaign has exploded in size and scope. Barely two dozen people attended Fonda’s first protest. On Friday, at a rally targeting the financial sector, she spoke to what looked like 500 protesters: mothers carrying infants, college students in pink hats, octogenarians like Fonda who brought their own stools to sit on as they shouted “Green New Deal” into the chilly January air.

“We’re building an army, folks,” Fonda proclaimed.

During the rally, actors Joaquin Phoenix and Martin Sheen spoke alongside indigenous activist Tasina Smith, community banker Kat Taylor and writer Naomi Klein.

“Fire Drill Fridays has created this entry point, an on-ramp, for people sitting in their homes desperate to do something,” Klein said.

Among the crowd was Fran Cohen, a 68-year-old fan of Fonda’s who spent her youth marching for various political causes. But she hadn’t attended a protest in decades — until she began attending Fire Drill Fridays.

“That Jane moved here to do this, I had to come to say thank you to her,” Cohen said. “And now I want to keep doing it.”

All told, organizers said, more than 1,000 people have attended the weekly events and roughly 600 of them have been arrested for the cause, including Sheen, Phoenix and Klein this Friday.

“We didn’t know what to expect when we started,” Fonda said. “But I think people were waiting to be given something do, and [Fire Drill Friday] was the right thing at the right time.

“We wanted to move people who were concerned but not active into the activism column, and I think we succeeded,” she said.

Fonda flies back to Los Angeles this weekend to begin filming the seventh season of her Netflix show “Grace and Frankie.” But her protest will continue in a new form, Greenpeace Executive Director Annie Leonard said. The group is helping to organize monthly rallies in California, and it is about to roll out a website with resources to help people organize events in their hometowns.

When, during her “Late Show” appearance on Monday, Fonda promoted a helpline that people could text for assistance planning their own climate protest, she got more than 3,000 responses.

Meanwhile, McKibben’s organization, 350.org, along with Sierra Club and a slate of other environmental groups, is launching a campaign calling on financial institutions to stop funding fossil-fuel projects. According to a report by the Rainforest Action Network, banks have provided nearly $2 trillion in financing for fossil-fuel projects since 2016. JPMorgan Chase was the largest contributor, providing $196 billion for coal mining, fracking and oil and gas projects from the deep ocean to the Arctic.

McKibben’s group has a list of more than 1,000 bank branches they aim to target in the coming months. “This marks an escalation of Fire Drill Friday,” he told the rally, speaking over a phone line from inside the Chase branch. “We’ve got to be here because ... they are the ones paying for the carbon bomb.”

“The two centers of power in this world are political and financial,” he said in an interview later. On Friday, he said, climate activists took their fight to both places.

Fonda has activist credentials that go back to the 1970s, when she rallied for working mothers and marched against the Vietnam War. But she has said her climate awakening came after reading about 16-year-old Swedish activist Greta Thunberg, whose weekly strike in front of her country’s parliament sparked a global youth movement.

“She realized what was happening and that this was barreling at us like an engine,” Fonda told The Washington Post in October. “It rocked me, because I knew that Greta had seen the truth. And the urgency came into my DNA the way it hadn’t before.”

She moved to Washington and got a permit to protest on the Capitol’s southeast lawn. She reached out to leaders of Black Lives Matter and the Sunrise Movement and began lobbying her Hollywood friends to fly out. She organized online “teach-ins” at which scientists would explain various aspects of climate change.

And she knew she wanted to get arrested, because nothing else seemed to be working.

“We’ve been petitioning and writing and marching and begging the government and they don’t hear,” Fonda said in an interview with Stephen Colbert on “The Late Show” earlier this week. “That’s why we’re engaging in civil disobedience.”

Fonda herself has been detained five times for public disturbance. After her fourth arrest — when she was held overnight at D.C. jail — she said an officer told her, “There‘s gotta be better ways to call attention to your cause. Don’t come back.”

“I think she’s right,” Fonda told The Post at the time. “My bones hurt.”

Nevertheless, on Dec. 20, the day before her 82nd birthday, she was detained again.

Washington’s young climate activists, many of whom have been protesting on Fridays for more than a year, say they welcome Fonda and the influx of older demonstrators who have followed her.

“It’s nice to see so many parents and grandparents,” said 17-year-old Jerome Foster II, who is in his 11th month of striking outside the White House. “People who can make a difference.”

Although young people hold the moral authority on climate issues, he added, it’s helpful to be joined by activists with bank accounts, driver’s licenses and the ability to vote. “And it’s cool they can get arrested,” he said with a grin.