MELVILLE - It has been 70 years since a top secret mission credited with ending World War II.

News 12 Long Island's Virginia Huie sat down with a Melville scientist about his work on the World's Greatest Secret. In 1944, Army Reserve Private Meyer Steinberg answered the call to duty to help create the world's first nuclear weapon. The code name for the top secret mission was "The Manhattan Project."

The Manhattan Project was set in motion in 1939 when Albert Einstein sent a letter to President Franklin D. Roosevelt warning that Nazi Germany was conducting nuclear weapons research.

The race for the U.S. to develop atomic weapons gained momentum after the 1941 bombing of Pearl Harbor.

Steinberg was 19 years old and a recent chemical engineering graduate when he began building the A-bomb. He was assigned to work on calculations, equipment inspection and making plutonium.

On July 16, 1945, Steinberg and the other scientists signed a document after witnessing the first atomic bomb test near Los Alamos, New Mexico. And on August 6, 1945, the U.S. unveiled the "World's Greatest Secret" by unleashing it over Hiroshima.