Los Alamos and the Manhattan Project: From a Secret Mesa to Trinity

At 5:29 a.m. Mountain War Time on July 16, 1945, a flash of light visible more than 160 miles away lit the New Mexico desert, followed by a huge fireball and mushroom cloud. The first nuclear explosion left a crater more than half a mile wide and turned the sand at ground zero into glass, or trinitite. "We knew the world would not be the same," J. Robert Oppenheimer recalled. "A few people laughed, a few people cried, most people were silent."

The Los Alamos main gate, 1943. Credit: U.S. Department of Energy.

A secret laboratory

On April 20, 1943, the University of California signed a contract with the U.S. Army Corps of Engineers to run a secret laboratory in the mountains of northern New Mexico. General Leslie Groves, appointed to lead the Manhattan Project in September 1942, wanted top scientists from across the country, and chose Oppenheimer — a respected teacher at the University of California, Berkeley, and the California Institute of Technology — to lead it. The two had very different management styles, but the partnership worked.

J. Robert Oppenheimer. Credit: U.S. Department of Energy.

Oppenheimer recruited most of the staff himself, visiting Cornell, Princeton, MIT, the University of Chicago and Berkeley, and most were eager to come. By spring 1943 they had arrived at the isolated mesa, once the site of a boys' preparatory school, often bringing their own research equipment. Oppenheimer set up four divisions:

Life behind the gate

Secrecy came first, but life had its normal side: families shared meals, hiked, and went to weekend parties at scientists' homes inside the fence — while work went on assembling the world's first nuclear device.

Laundry day at Los Alamos. Credit: U.S. Department of Energy.

The Gadget

The Gadget was an implosion weapon: a core of plutonium, below critical mass, surrounded by high explosives that would crush it instantly into a critical mass. In September 1944 a test site was chosen on the Alamogordo Bombing and Gunnery Range, a flat, calm stretch of desert about 200 miles southeast of Los Alamos. That fall more than 250 workers began building the Trinity site — the name for both the test and the program — with three observation shelters, electric power, more than 50 cameras, and a 100-foot steel tower. On the morning of the test, an electric winch hauled the Gadget to the top.

Oppenheimer (second from left) oversees the final assembly of the Gadget. Credit: U.S. Department of Energy.

The Trinity test, 5:29 a.m., July 16, 1945. Credit: U.S. Department of Energy.

Hiroshima and Nagasaki

Trinity proved that a plutonium implosion weapon would work. On August 9, 1945, three days after the uranium bomb Little Boy exploded over Hiroshima, Japan, Fat Man — the plutonium implosion bomb developed at Los Alamos from the Gadget — exploded over Nagasaki. It was the first, and so far only, use of atomic weapons in war.

Sources

Based on "Manhattan Project Science at Los Alamos," National Park Service (Manhattan Project National Historical Park), a work of the United States government in the public domain. It cites Cynthia C. Kelly, ed., The Manhattan Project (2007), and Richard Rhodes, The Making of the Atomic Bomb (1986).