It was the bomb credited with ending World War II.
In Hiroshima, 80,000 people died instantly when the bomb was dropped on August 6, 1945, and another 112,000 died in the aftermath. More than 70,000 people died instantly when the second bomb was dropped on August 9 in Nagasaki.
The Manhattan Project, the federal military program where leading scientists developed the atomic bomb in secret, could become a national historic park with the help of recently passed congressional legislation.
The National Defense Authorization Act includes seven new national park sites, the expansion of nine national park sites and the extension of 15 National Heritage Areas. The legislation awaits President Barack Obama's signature.
"Our national parks are a reflection of our nation, both past and present, and these seven new national park sites will further tell America's stories," said Clark Bunting, president and CEO of the National Parks Conservation Association.
"Bipartisan, congressional approval for protecting and preserving Harriet Tubman's heroic life and work, Columbian mammoths and Ice Age fossils at Tule Springs, and the complexity of the Manhattan Project continue to make our National Park System our country's best idea," he said.
Here are some potential new and expanded park sites worth exploring.
Manhattan Project National Historical Park
Working in secret during World War II, scientists J. Robert Oppenheimer, Maria Goeppert Mayer and others led thousands of workers in Los Alamos, New Mexico; Oak Ridge, Tennessee; and Hanford, Washington, to build a nuclear reactor and assemble the atomic bomb. The legislation authorizes the proposed park, which would be located in all three states.
Its creation is dependent on land acquisition. While the National Park Service will interpret the sites for the public, the U.S. Department of Energy is responsible for ensuring safety, environmental remediation and historic preservation of its Manhattan Project properties, and access to the properties.
Harriet Tubman National Historical Park
Born into slavery in Maryland, Harriet Tubman escaped to Philadelphia and rose to become an iconic conductor on the Underground Railroad, returning again and again to Maryland to help enslaved people escape to freedom.
After the Civil War, she fought for women's suffrage along with Susan B. Anthony in Auburn, New York. The proposed national historical park, whose creation is also dependent on land acquisition, would include the existing Harriet Tubman National Monument on Maryland's Eastern Shore and add new sites in New York.
Tule Springs Fossil Beds National Monument
Once home to bison herds, prides of lions, Columbian mammoths, saber tooth cats, herds of bison and other Ice Age animals, Nevada's Tule Springs desert used to be lush wetlands. The evidence of its past is ripe for further exploration if the area becomes a new national park site as the Tule Springs Fossil Beds National Monument.
Valles Caldera National Preserve
The Valles Caldera National Preserve in New Mexico is "one of the world's best examples of a resurgent caldera and its large eruptions," says the National Parks Conservation Association. Calderas are vast sunken areas formed after supervolcano eruptions blow out the ground and the land falls back to rest. (Yellowstone may be the world's most famous supervolcano.) Visitors can also enjoy exploring the mountains, old growth timber and Native American heritage in the area. The site is already owned by the federal government, and it would get even more attention as a new national park site.
Gettysburg National Military Park
The Gettysburg Train Station, where President Abraham Lincoln arrived on a train to deliver the historic Gettysburg Address, would be added to the existing Gettysburg National Military Park. The train station also served as a field hospital during the Battle of Gettysburg. The Gettysburg Foundation owns the land, and there are plans to donate it to the National Park Service.