This image from 1945 shows Manhattan Project physicist Harold Agnew smiling and holding the plutonium core of one of the world's most devastating weapons.

Replica of the "Fat Man" bomb. Wikipedia Weighing 14 pounds and responsible for 80,000 deaths, the heart of the "Fat Man" atomic bomb was detonated on August 9, 1945, over the Japanese city of Nagasaki.

Fat Man was the second nuclear weapon to be deployed in combat after the US dropped a 5-ton atomic bomb, called "Little Boy," on the Japanese city of Hiroshima.

Agnew, who became the third director of the Los Alamos Laboratory, flew in a plane alongside the Enola Gay and took the only footage of the "Little Boy" attack from a bird's-eye view.

Here's a clip of the film he captured:

Footage of the "Little Boy" attack from a bird's-eye view. YouTube/Amanda Macias/Business Insider Three days later, the US dropped the Fat Man bomb on Nagasaki, prompting Japan to surrender to the Allied Forces, effectively ending World War II.

Of the 10,800-pound Fat Man bomb, about 2 pounds underwent a fission reaction, and a gram of that yielded an explosion equivalent to 21,000 tons of TNT, according to the Atomic Heritage Foundation.