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.

Truman, informed of this development, at first refused to believe it. He ordered his scientific and military advisers to recheck their data. Once they confirmed the results, however, Truman had to face the fact that America’s nuclear monopoly was gone. He also had to face the task of informing the American people, for the news was sure to leak. On September 23, he issued a brief statement to the media. “We have evidence,” the statement read, “within recent weeks an atomic explosion occurred in the USSR.” The president attempted to downplay the seriousness of the event by noting that “The eventual development of this new force by other nations was to be expected. This probability has always been taken into account by us.”

What had not been taken into account by the U.S. government was the fact that the Soviets, like the Americans, had captured many German scientists after World War II who had been working on nuclear development. In addition, the United States was unaware of the scope of Soviet spy efforts to gain valuable information. Years ahead of what Americans thought possible, the Soviets had exploded a nuclear device. Truman reacted by requesting an intensive re-evaluation of America’s Cold War policies by the National Security Council. The report, issued to the president in early 1950, called for massive increases in military spending and a dramatic acceleration in the program to develop the next stage of nuclear weaponry—the hydrogen bomb.