Dent Thompson had never heard of Samaritan’s Purse when the Christian relief group called last month and asked for his help.

Samaritan’s Purse and another global ministry group, SIM, were scrambling to transport two ­Ebola-stricken U.S. missionaries from Liberia to Emory University Hospital in Atlanta for treatment. They had learned from government officials that Thompson’s company, Georgia-based Phoenix Air Group, had a specially designed Gulfstream III with a one-of-a-kind isolation unit developed precisely for emergency medical evacuations. They wanted to send the plane to West Africa right away.

“They were beyond distraught that two of their people were stuck in Africa with no apparent way to get them out of there,” Thompson recalled. “Samaritan’s Purse indicated to us that they would hire anybody with the ability to pull them out. . . . We gave them a price, and they agreed to the price.”

The drastic measures to rescue the missionaries point to the global reach and deep pockets of Samaritan’s Purse, which last year raised hundreds of millions of dollars in contributions and received tens of millions in federal grants. Though the group has a relatively low profile in the United States, it operates on the front lines of public health crises and natural disasters around the world.

The Ebola outbreak has made it clear how much governments, especially those of poorer countries, rely on nonprofit groups to deliver medical care and supplies and sound an early alert on emerging health crises. That has brought attention to Samaritan’s Purse, a sometimes controversial group run by Franklin Graham, the son of the Rev. Billy Graham.

Three Ebola survivors from Liberia were interviewed by the World Health Organization on July 17, 2014. They describe their symptoms, who they contracted the disease from and their paths to recovery. (World Health Organization)

Driven by a desire to spread the Christian message, the nonprofit is a sophisticated international enterprise, able to navigate the logistical and regulatory challenges necessary to rescue stricken missionaries and gain access to a promising experimental treatment that was administered to the workers.

Phoenix Air’s Thompson declined to disclose the price for evacuating the two missionaries — Kent Brantly, a doctor with Samaritan’s Purse, and Nancy Writebol, who along with her husband was working for SIM at a hospital in Liberia. SIM President Bruce Johnson has said publicly that the relief groups have spent more than $2 million on the transport and treatment of the missionaries, though a spokesman for Samaritan’s Purse said that the organization had spent roughly $1.5 million on all Ebola response in Liberia. Whatever the actual cost, it wasn’t a cheap undertaking.

“This came straight out of their bank account,” Thompson said of the two air ambulance flights his company provided, noting that the U.S. government helped only with logistics. “You can’t do this unless you are very well financed. This is not the local Humane Society asking for donations.”

Ken Isaacs looked stern as he began his testimony before a House committee earlier this month.

“The Ebola outbreak has had a profound impact on our organization,” Isaacs, a vice president at Samaritan’s Purse and a former director of the foreign disaster assistance arm of the U.S. Agency for International Development, told lawmakers. “We were devastated to discover that two of our personnel had contracted the deadly virus while trying to assist others.”

He recounted how the group received help from staffers at the Centers for Disease Control and Prevention and the National Institutes of Health in tracking down and securing ZMapp, an experimental Ebola treatment, to send to the two infected U.S. missionaries. He thanked by name officials at the State Department and the Defense Department and in Congress for helping with the evacuations of Brantly and Writebol.

During the deadliest Ebola outbreak ever in western Africa, two American missionaries received an experimental drug called ZMapp. An Ebola expert explains how ZMapp is derived and how it fights the deadly virus. (Gillian Brockell and Pamela Kirkland/The Washington Post)

Samaritan’s Purse and SIM are “nongovernmental organizations,” or NGOs, operating internationally. In an informal partnership, Samaritan’s Purse helps staff hospitals run by SIM in Africa. Because of the Ebola outbreak, the two groups have evacuated dozens of “nonessential” personnel from Liberia. Still, Samaritan’s Purse has 350 staff members, mostly African nationals, remaining in Liberia, providing support at two clinics and working on public awareness campaigns, said a spokeswoman for the group.

With headquarters on a country road outside of Boone, N.C., in the Blue Ridge Mountains, Samaritan’s Purse has neither the big name nor the pocketbook of such groups as Doctors Without Borders and CARE International, a global humanitarian agency. But its most recent financial disclosures detail what a well-funded, far-reaching organization it has become in the 35 years since Franklin Graham took the helm.

Last year, the group had roughly $460 million in revenue, records show. It maintains offices in Canada, Australia and the United Kingdom and has more than a dozen aircraft situated around the world, including two helicopters, to shuttle around ministry staff and to help reach remote communities or those hard-hit by natural disaster.

While significantly smaller, SIM began operating in Africa in the late 19th century, with the goal of bringing Christianity to tens of millions of people in sub-Saharan Africa. Today, the group has more than 1,600 active missionaries working in dozens of countries. They often are supported financially by their own churches and team up with workers from other NGOs.

A big chunk of the Samaritan’s Purse budget each year goes toward Operation Christmas Child, an effort that since 1993 has provided more than 100 million gift-filled shoe boxes to children in 112 countries. But much of the remaining budget goes toward medical missions and relief efforts in some of the poorest and most war-torn corners of the world, such as Africa, Asia and South America.

The organization, which is nondenominational, has rebuilt churches and provided humanitarian assistance to hundreds of thousands of people affected by the civil war in South Sudan. Its medical arm helped to staff dozens of hospitals in nearly 30 countries last year. The group has ramped up relief efforts in Iraq, sending food, shelter and clothing to thousands of families fleeing violent Islamic militants. The group also does work in the United States — for example, it helped provide housing in the wake of Hurricanes Sandy and Katrina.

The growing worldwide ministry of Samaritan’s Purse has not been free of controversy.

During the 1990-1991 Gulf War, Franklin Graham drew a sharp rebuke from Gen. Norman Schwarzkopf after the group tried to arrange for U.S. troops stationed in Saudi Arabia to distribute thousands of Arabic-language Bibles — an undertaking that violated an agreement between the Saudi and American governments to avoid proselytizing.

In 2001, the New York Times detailed how Samaritan’s Purse, which had received more than $200,000 from USAID, had “blurred the lines between church and state” by proselytizing while helping victims of an earthquake in El Salvador. An official for the group said it did not discriminate in who received aid and that the government knew its role as a faith-based organization. “We are first a Christian organization and second an aid organization,” the official said at the time. “We can’t really separate the two.” The group ultimately was found not to have violated federal guidelines.

Graham himself has proven a polarizing figure over the years. He stirred widespread criticism after the Sept. 11, 2001, terrorist attacks when he referred to Islam as a “wicked” and “evil” religion. More recently, he has sharply criticized President Obama’s support for same-sex marriage, while applauding a Russian law that bans gay “propaganda.” In 2012, he apologized after raising doubts about Obama’s Christian faith, saying he regretted any comments “which may have cast any doubt on the personal faith of our president.” The group declined interview requests for this report.

Those controversies aside, Smart Money magazine has named Samaritan’s Purse the most efficient religious charity numerous times, and the group maintains a reputation of being among the first to combat the worst public health crises around the world.

“Given the remote and hard-to-reach areas they work in, there’s been many instances in the past where we’ve first heard of specific suspected clusters of illnesses through them,” Rima Khabbaz, the CDC’s deputy director for infectious diseases, said of NGOs such as Samaritan’s Purse. “They are no doubt very important partners in our global public health work. Not infrequently, [the] first unconfirmed reports reach the public health community through them.”

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said in many parts of the world, groups such as Samaritan’s Purse and Doctors Without Borders “are the safety net for global health.” He added: “They are the ones in the areas of war and civil unrest.”

On Capitol Hill this month, Isaacs reiterated that role and criticized the slow international response to the recent outbreak.

“The Ebola crisis was not a surprise to us at Samaritan’s Purse. We saw it coming back in April,” he said, adding: “The international response to the disease has been a failure. . . . If there was any one thing that needed to demonstrate a lack of attention of the international community on this crisis, which has now become an epidemic, it was the fact the international community was comfortable in allowing two relief agencies to provide all of the clinical care for Ebola victims in three countries. . . . It was not until July 26th, when Kent Brantly and Nancy Writebol were confirmed positive, that the world sat up and paid attention.”

The desperate effort by Samaritan’s Purse to rescue Brantly and Writebol seems to have paid off. Both have improved steadily and are likely to be released from the hospital any day.

Brantly wrote last week from his hospital room that he looks forward to reuniting soon with his wife and children. He asked for prayers for those in West Africa still suffering in the Ebola crisis, saying, “Their fight is far from over.”

Writebol enjoyed a tearful reunion last weekend with her husband, David, who had waited out a quarantine period in Charlotte before rushing to Atlanta to see her. Still unable to touch, they placed their hands on opposite sides of the glass that separated them and shared a prayer of thanks.