Moxie, age 13 in Winthrop, Mass., ten years after searching for survivors of the 9/11 attack at the World Trade Center in New York City (© Charlotte Dumas/Barcroft Media/Landov)

Moxie, now 13, from Winthrop, Mass., spent eight days at Ground Zero.

Kaiser, age 12, at home ten years after searching for survivors of the 9/11 attack at the World Trade Center in New York City (© Charlotte Dumas/Barcroft Media/Landov)

Kaiser, 12, from Indianapolis, helped first responders at the site of the World Trade Center.

Red, age 11, in Annapolis Md., ten years after searching for survivors of the 9/11 attack at the World Trade Center in New York City (© Charlotte Dumas/Barcroft Media/Landov)

Red, 11, from Annapolis, Md., searched for survivors at the Pentagon.

Guinness, age 15, in Highland Calif., ten years after searching for survivors of the 9/11 attack at the World Trade Center in New York City (© Charlotte Dumas/Barcroft Media/Landov)

Guinness, 15, from Highland, Calif., sifted through the rubble for more than a week

A rescue dog searches for survivors of the 9/11 attack at the World Trade Center in New York City, 2001 (© Blake Wallis/Barcroft Media/Landov)

This unidentified dog was just one of nearly 100 who scoured the site for days.

Commemorate the four-legged heroes who saved lives on Sept. 11

9/11/2012

Humans weren't the only first responders to the site of the World Trade Center on Sept. 11, 2001. Search dogs played an invaluable role in helping emergency crews locate and rescue survivors, and like their human counterparts, they often worked days on end without taking a break. Hundreds of dogs helped, but only a handful still survive, and photographer Charlotte Dumas set out to take portraits of them to commemorate their service more than a decade later. Dumas compiled the photos for a book titled "Retrieved," which came out last year and marked the 10th anniversary of the attacks. Check out our gallery of her shots to honor these four-legged heroes.

Check out the msnNOW.com homepage to read more trending stories.