COUNTDOWN TO TRINITY

December 1938: Two scientists in Berlin unintentionally split a uranium atom, unlocking the possibility of nuclear weapons.

Sept. 1, 1939: Germany invades Poland, starting World War II.

October 1939: President Franklin D. Roosevelt gets a letter, signed by Albert Einstein, alerting him to the perilous potential of atomic weapons.

Dec. 7, 1941: Japan attacks U.S. Navy base at Pearl Harbor, pulling America into World War II.

September 1942: U.S. Army Brig. Gen. Leslie R. Groves takes charge of the Manhattan Project to develop nuclear weapons.

November 1942: Los Alamos Ranch School property selected as location for Site Y complex for building atomic bombs.

February 1943: Physicist J. Robert Oppenheimer officially chosen to lead Site Y scientific team.

March 1943: Scientists start to arrive at Site Y in Los Alamos.

November 1943: Construction of Manhattan Project facilities completed at Los Alamos.

July 16, 1945: Atomic bomb successfully tested at Trinity Site in New Mexico.