President Truman announces Soviets have exploded a nuclear device | September 23, 1949 | HISTORY

In a surprisingly low-key and carefully worded statement, President Harry S. Truman informs the American people that the Soviets have exploded a nuclear bomb. The Soviet accomplishment, years ahead of what was thought possible by most U.S. officials, caused a panic in the American government.

The United States developed the atomic bomb during the latter stages of World War II and dropped two bombs on Japan in August 1945. By the time of the bombings in Japan, relations between the United States and the Soviet Union were already crumbling. Many U.S. officials, including President Truman, came to see America’s atomic monopoly as a valuable asset in the developing Cold War with Russia. Most American officials, and even the majority of scientists in the United States, believed that it would be many years before the Soviets could develop an atomic bomb of their own, and by that time the United States would have achieved a vast numeric superiority. On September 3, 1949, however, U.S. scientists recorded seismic activity from inside the Soviet Union that was unmistakably the result of an underground nuclear test.