On one of the most tragic days in American history, brave heroes, including law enforcement officers, firefighters and innocent civilians, banded together to safeguard one another and escape the collapsing World Trade Center in New York City, which was surrounded by a deadly accumulation of smoke and debris.

Among the heroes who joined the relief efforts in the aftermath of the terrorist attack on the U.S. on Sept. 11, 2001, unbeknownst to them, were hundreds of dogs, alongside their handlers, who relentlessly searched for any living persons and the bodies of those who lost their lives in the wreckage.

The unfathomable tragedy which took the lives of nearly 3,000 people elicited a global response.

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Rubble full of hazardous materials lay where the north tower and south tower of the World Trade Center once stood tall. Workers from government and volunteer organizations echoed patriotism and selflessness and joined one another to support the rescue efforts following the terrorist attacks that shook the nation’s history.

Bonded by a love for the country and respect for the fallen, the responsibilities of both dogs and their handlers at Ground Zero varied in the nine months after the deadliest attack on America.

1. Handler Denise Corliss and Bretagne, a golden retriever
2. Handler Frank Shane and Nikie, a golden retriever
3. Handler Bobbie Snyder and Willow, a Labrador retriever

Handler Denise Corliss and Bretagne, a golden retriever

Bretagne, pronounced Brittany, was an American Kennel Club-registered golden retriever and a member of Texas A&M Task Force 1 (TX-TF1). Following months of training, she became a certified member of the FEMA Search and Rescue Canine team.

Her handler, Denise Corliss, has maintained her position on TX-TF1 since 2000, and worked with Bretagne during her first official deployment to Ground Zero after the catastrophic events.

Bretagne’s responsibility was “to use her keen sense of smell to locate survivors in, often, immense piles of debris or water,” Merribeth Kahlich, a spokesperson for TX-TF1, told Fox News Digital.

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She went on to receive the Hero Dog Award for Search and Rescue in 2014. The honor is presented to canines who “do extraordinary things, such as saving lives on the battlefield, lending sight or hearing to a human companion or simply being a friend to their human companions,” according to Kahlich.

During Bretagne’s 11 years of service as a Live-Find Canine Search Specialist, she also worked at the disaster sites of Hurricanes Erica, Ivan, Dennis, Katrina, Rita, Ernesto, Dean and Gustav, and the 2002 Olympics in Salt Lake City.

Though it is undisclosed whether Bretagne recovered any survivors or victims from the 9/11 terror attacks, Kahlich said that she worked at Ground Zero opposite Corliss for 10 days and often collected a meager four hours of sleep before going back to work.

“When Bretagne and Denise waited for their next search area assignment, Bretagne took on the unexpected role of therapy dog,” Kahlich said.

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“She seemed to know who needed the comfort of a pup, which firefighter needed to hold her close and stroke her fur. She was affectionate and fiercely devoted to Denise, she rarely took her eyes off her.”

Bretagne was 2 years old when she combed through the wreckage of fallen buildings in Lower Manhattan. She retired at age 9, though Kahlich said she was not content with relaxing and went on to become a “reading dog” at a Texas elementary school, where she was a reading partner for many first-graders.

The Texas canine and companion to both Corliss and her husband, Randy, lived to be 16 years old before dying on June 6, 2016. She did not suffer any ailments associated with her deployment to Ground Zero, according to Kahlich.

“After passing, her body continued in service through her tissue sample donations that became a part of the 9/11 Canine Search and Rescue dog study at the Penn Vet Working Dog Center,” Kahlich said. “This research will help scientists better understand the long-term effects of canines who served during the 9/11 disaster.”

Corliss remains an active handler on TX-TF1 and serves FEMA as a canine evaluator and instructor.

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Handler Frank Shane and Nikie, a golden retriever

On the morning of Sept. 11, 2001, Frank Shane, a certified trauma responder, was woken by his neighbor tapping on his front door politely asking for a ride to work in New York City.

“It was a beautiful day,” Shane told Fox News Digital.

While he was not in a rush to get back home, Shane stopped his truck with Nikie, a K-9 disaster relief therapy dog riding shotgun, to look out over the clear skies above the Hudson River.

“It was almost like a picture, postcard type of day, where the sky was so blue and things were calm,” he said. “It was very peaceful.”

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Shane said, at the time, he was aware the deafening sound he heard was a jet engine at full throttle, but it was not until recently that the crashing blow of American Airlines Flight 11 into the north tower of the World Trade Center came flooding back to him.

“All of a sudden, I had a flashback to the sound I heard that day,” Shane said. “I had repressed it.”

Shane recalled the panic and alarm carried out in the faces of typically resilient New Yorkers.

The next morning, again with Nikie by his side, Shane returned to the West Side Highway in hopes of making it to Ground Zero to volunteer his services. A New York Port Authority officer stopped Shane’s Jeep, as he recognized Nikie from the day before.

“He patted Nikie and said, ‘Go ahead, they need you,’” Shane said. “I didn’t know what my job was going to be.”

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Shane strapped on Nikie’s work boots and vest and showed up to Ground Zero for nine months, until May 30, 2002, when the “last column” among the rubble and destruction was removed.

“Every day, Nikie started to become part of the fabric down there,” Shane said. “People needed him. Even some of the search and rescue handlers were depressed, and their dogs were depressed because they weren’t finding anybody.”

Nikie had experience emotionally supporting traumatized or sick individuals, and Shane knew he loved his job, though this particular assignment was not official in nature. During Nikie’s training to become a therapy dog, Shane said he failed the last certification test 10 times.

“He did everything perfectly, but he learned how to flunk the last test,” Shane said. “Finally, they just made him a therapy dog.”

Victim’s family members would show up to respite areas desperately seeking answers regarding their loved ones, and Shane said they trusted Nikie and opened up to him. He added that when his responsibilities of restoring peace and hope among workers and volunteers came to an end, Nikie went into a depression and refused food.

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“He didn’t know why he wasn’t going back the next day,” Shane said. “He had a lack of a sense of purpose.”

Shane rustled up worthwhile tasks for Nikie to resurrect his joy for giving.

Nikie fell very ill with an aggressive cancer, which Shane revealed is the illness that took most of the canine’s lives who worked at Ground Zero.

“He died quickly,” Shane said. “In a way, he didn’t suffer.”

Nikie passed away in 2004. Shane donated Nikie’s uniform, including his vest and booties still soiled in dirt and debris, to the National 9/11 Memorial & Museum in New York City.

Handler Bobbie Snyder and Willow, a Labrador retriever

Like millions of Americans across the country on Sept. 11, 2001, Bobbie Snyder watched in horror and anguish as the news surrounding the terrorist attacks on U.S. soil unfolded with her husband at their home in Pennsylvania.

A sentiment which echoed across America, Snyder was adamant on helping. It was clear she would soon deploy to New York City with her yellow Labrador, Willow, to aid in disaster relief efforts.

“We saw what happened, that this plane went into the tower,” Snyder told Fox News Digital. “I looked at my husband and I said ‘You’re going to have to take daddy to the doctor because I have to pack up my gear.’”

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Snyder’s father was scheduled for a doctor’s appointment later that morning, but her priorities shifted upon the impact of the first plane. That night, Snyder drove to Harrisburg, where her team, Pennsylvania Task Force One (PA-TF1), gathered together before deploying.

“That evening, we arrived in New York City,” she said.

Willow and Snyder first bravely worked together in the aftermath of the Oklahoma City bombing in 1995, an act of homegrown terrorism which killed 168 people, according to the FBI website.

“We didn’t go out until the following morning,” Snyder added. “It was like nothing I ever expected.”

PA-TF1 was divided into groups which alternated working 12-hour shifts on and 12-hour shifts off.

“Our dogs were there to find the missing,” Snyder said.

“Across the river was the kill field, and they took everything they found,” she recalled. “They had dogs over there that were cadaver dogs. People were bringing toothbrushes, hairbrushes, to find [the] remains of their families. People were lined up in the street with pictures of their family, asking ‘Please, help me find my family member.’”

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Snyder added, “We were told that that was our job, was to find our firemen and to get as many remains as we could. We did it as a team.”

For two to three weeks, 5-year-old Willow scoured the rubble off her leash and used training, including a bark alert, to identify if she had found human remains for Snyder.

“When they sent us down they said ‘This is your area, and we want you to search.’ I was like ‘Where do we begin?’ It was just unbelievable. It was just rubble all over.”

Snyder, now a New Jersey resident, was experienced working in the medical field and said she was used to seeing people in various conditions. Though, she added that her PA-TF1 training required many certifications which readied her for relief amid disaster events.

“You couldn’t do it, or you did it,” Snyder said. “I lived so close to New York, I was asked if I would go periodically up to New York.”

Though PA-TF1 was relieved by TX-TF1, Snyder and Willow continued their relief efforts at Ground Zero and were put up at the Ritz-Carlton.

“They couldn’t be nicer to us,” she said. “We always had clean uniforms, and you can’t usually leave dogs in the hotel, but because they were the 9/11 dogs, they left us. They just loved having us there.”

Despite the destruction and asbestos, neither Snyder, 78, nor Willow endured the health consequences of searching through the ruins at Ground Zero.

“Unfortunately, we have lost some members of our team, though,” Snyder said.

Willow lived a long life and passed away from natural causes when she was 15 years old.