By early August 1945, the United States had been actively fighting in World War II for nearly four years. Much of that fighting had been far across the Pacific Ocean against the Japanese military, which had directly attacked US forces at Pearl Harbor, Hawaii, in December 1941. In Europe, Allied troops had already forced first Italy and then Germany to surrender, but warfare seemed likely to rage on for a while in the Pacific before the Japanese could be subdued. Military analysts estimated that a direct attack on the Japanese islands could cost the United States some one hundred thousand casualties. President Harry S. Truman, who had been in office just four months, decided to use a powerful new weapon to hasten the end of the conflict: the atomic bomb. US troops dropped the first atomic bomb on the city of Hiroshima on August 6, 1945, devastating the city and its populace. A second such attack on Nagasaki preceded the Japanese offer to surrender on August 10.

By early August 1945, the United States had been actively fighting in World War II for nearly four years. Much of that fighting had been far across the Pacific Ocean against the Japanese military, which had directly attacked US forces at Pearl Harbor, Hawaii, in December 1941. In Europe, Allied troops had already forced first Italy and then Germany to surrender, but warfare seemed likely to rage on for a while in the Pacific before the Japanese could be subdued. Military analysts estimated that a direct attack on the Japanese islands could cost the United States some one hundred thousand casualties. President Harry S. Truman, who had been in office just four months, decided to use a powerful new weapon to hasten the end of the conflict: the atomic bomb. US troops dropped the first atomic bomb on the city of Hiroshima on August 6, 1945, devastating the city and its populace. A second such attack on Nagasaki preceded the Japanese offer to surrender on August 10.

In 1939, a group of physicists began lobbying the US government to fund development of a new bomb that employed a process known as nuclear fission, which released energy by breaking the bonds between atoms. German-born scientist Albert Einstein convinced President Franklin D. Roosevelt of its military potential, and beginning in 1942 a cadre of scientists and support workers strove to develop an atomic weapon using radioactive elements such as uranium and plutonium. Their efforts were known as the Manhattan Project. Beginning in 1943, much of the practical work happened at a remote laboratory in New Mexico, all while US troops fought alongside the Allies to repel Germany, Italy, Japan, and other Axis forces in North Africa, Europe, and the Pacific. Roosevelt’s death in the spring of 1945 left his vice president, Harry S. Truman, at the helm of the nation’s military. On July 16, 1945, at a New Mexico air base, scientists conducted the first successful nuclear bomb explosion.

Shortly after the test confirmed the functionality of the atomic bomb, Truman joined Great Britain’s outgoing prime minister Winston Churchill and Soviet premier Joseph Stalin at Potsdam, Germany. The victorious Allied leaders spent much of the conference planning for postwar peace in Europe, but they also discussed how to conclude the war against Japan in the Pacific. Historians generally agree that Truman’s confidence in the atomic bomb as a destructive force informed his strong negotiating stance at the conference; certainly, he hinted to Stalin, whom he recognized as a future competitor for global influence, that the United States had the weapon. Although never specifically mentioned, the atomic bomb was the underlying threat issued against Japan in the Potsdam Declaration by the United States, Great Britain, and China on July 26, 1945. This declaration announced the terms on which the Allies would accept a Japanese surrender and warned that “the alternative for Japan is prompt and utter destruction.” These terms included the unconditional surrender and complete disarmament of Japan’s military and its leaders, followed by a period of Allied occupation and rebuilding.

The Japanese refused to accept these terms, and Truman was then faced with the choice of whether to use the atomic bomb to force an unconditional surrender or to begin a traditional land and sea attack that was estimated to take months and cost tens of thousands of US lives. Truman chose the former, and on the morning of August 6, the US bomber Enola Gay dropped an atomic bomb on the city of Hiroshima.

A native of Missouri, Harry S. Truman served in World War I and operated a men’s clothing store before beginning a political career as an elected county judge in 1922. He made the jump to the US Congress with election as Missouri’s junior Democratic senator in 1934 at the height of the New Deal. Truman built on his reputation for honesty and fair dealing, and in 1944 he was tapped as the running mate for President Franklin D. Roosevelt in his effort to win an unprecedented fourth term. Roosevelt and Truman had little personal or professional relationship, however, and Roosevelt’s administration had shared little to no detail about pressing defense or diplomatic concerns when Truman unexpectedly became president upon Roosevelt’s death in April of 1945. As president, Truman suddenly faced the challenges of concluding World War II, managing increasingly tense relations with the Soviet Union, and preparing the nation to begin to return to a peacetime footing.

Sixteen hours ago an American airplane dropped one bomb on Hiroshima and destroyed its usefulness to the enemy. That bomb had more power than 20,000 tons of TNT. It had more than two thousand times the blast power of the British “Grand Slam” which is the largest bomb ever yet used in the history of warfare.

The Japanese began the war from the air at Pearl Harbor. They have been repaid many fold. And the end is not yet. With this bomb we have now added a new and revolutionary increase in destruction to supplement the growing power of our armed forces. In their present form these bombs are now in production and even more powerful forms are in development.

It is an atomic bomb. It is a harnessing of the basic power of the universe. The force from which the sun draws its power has been loosed against those who brought war to the Far East.

Before 1939, it was the accepted belief of scientists that it was theoretically possible to release atomic energy. But no one knew any practical method of doing it. By 1942, however, we knew that the Germans were working feverishly to find a way to add atomic energy to the other engines of war with which they hoped to enslave the world. But they failed. We may be grateful to Providence that the Germans got the V-1’s and V-2’s late and in limited quantities and even more grateful that they did not get the atomic bomb at all.

The battle of the laboratories held fateful risks for us as well as the battles of the air, land, and sea, and we have now won the battle of the laboratories as we have won the other battles.

Beginning in 1940, before Pearl Harbor, scientific knowledge useful in was pooled between the United States and Great Britain, and many priceless helps to our victories have come from that arrangement. Under that general policy the research on the atomic bomb was begun. With American and British scientists working together we entered the race of discovery against the Germans.

The United States had available the large number of scientists of distinction in the many needed areas of knowledge. It had the tremendous industrial and financial resources necessary for the project and they could be devoted to it without undue impairment of other vital war work. In the United States the laboratory work and the production plants, on which a substantial start had already been made, would be out of reach of enemy bombing, while at that time Britain was exposed to constant air attack and was still threatened with the possibility of invasion. For these reasons Prime Minister Churchill and President Roosevelt agreed that it was wise to carry on the project here. We now have two great plants and many lesser works devoted to the production of atomic power. Employment during peak construction numbered 125,000 and over 65,000 individuals are even now engaged in operating the plants. Many have worked there for two and a half years. Few know what they have been producing. They see great quantities of material going in and they see nothing coming out of these plants, for the physical size of the explosive charge is exceedingly small. We have spent two billion dollars on the greatest scientific gamble in history — and won.

But the greatest marvel is not the size of the enterprise, its secrecy, nor its cost, but the achievement of scientific brains in putting together infinitely complex pieces of knowledge held by many men in different fields of science into a workable plan. And hardly less marvelous has been the capacity of industry to design and of labor to operate, the machines and methods to do things never done before so that the brainchild of many minds came forth in physical shape and performed as it was supposed to do. Both science and industry worked under the direction of the United States Army, which achieved a unique success in managing so diverse a problem in the advancement of knowledge in an amazingly short time. It is doubtful if such another combination could be got together in the world. What has been done is the greatest achievement of organized science in history. It was done under pressure and without failure.

We are now prepared to obliterate more rapidly and completely every productive enterprise the Japanese have above ground in any city. We shall destroy their docks, their factories, and their communications. Let there be no mistake; we shall completely destroy Japan’s power to make war.

It was to spare the Japanese people from utter destruction that the ultimatum of July 26 was issued at Potsdam. Their leaders promptly rejected that ultimatum. If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on this earth. Behind this air attack will follow sea and land forces in such number that and power as they have not yet seen and with the fighting skill of which they are already well aware.

The Secretary of War, who has kept in personal touch with all phases of the project, will immediately make public a statement giving further details.

His statement will give facts concerning the sites at Oak Ridge near Knoxville, Tennessee, and at Richland, near Pasco, Washington, and an installation near Santa Fe, New Mexico. Although the workers at the sites have been making materials to be used producing the greatest destructive force in history they have not themselves been in danger beyond that of many other occupations, for the utmost care has been taken of their safety.

The fact that we can release atomic energy ushers in a new era in man’s understanding of nature’s forces. Atomic energy may in the future supplement the power that now comes from coal, oil, and falling water, but at present it cannot be produced on a bases to compete with them commercially. Before that comes there must be a long period of intensive research. It has never been the habit of the scientists of this country or the policy of this government to withhold from the world scientific knowledge. Normally, therefore, everything about the work with atomic energy would be made public.

But under the present circumstances it is not intended to divulge the technical processes of production or all the military applications. Pending further examination of possible methods of protecting us and the rest of the world from the danger of sudden destruction.

I shall recommend that the Congress of the United States consider promptly the establishment of an appropriate commission to control the production and use of atomic power within the United States. I shall give further consideration and make further recommendations to the Congress as to how atomic power can become a powerful and forceful influence towards the maintenance of world peace.

President Truman’s announcement on August 6, 1945, that the United States had dropped a powerful new kind of weapon on the Japanese city of Hiroshima stunned the world. His statement combines the need to inform the American people of the actions of its military with the goal of warning foreign enemies that this action signals the willingness of the US military to win an unconditional victory in World War II at almost any cost. Truman’s rhetoric thus emphasizes the technological and military superiority of the United States while conveying a threat of continued atomic action against Japan.

Truman opens with an assertion of the power of the bomb dropped on Hiroshima and then compares its force to the commonly known explosive TNT. He immediately justifies the use of such a weapon against Japan as a countermeasure for that nation’s air attack on Pearl Harbor years before. Truman is clear that this new weapon is now part of the US arsenal and that the nation is willing to use it again if necessary.

Next, he explains how such an advanced piece of weaponry came about by revealing the previously secret work and scope of the Manhattan Project, which was essential to the Allied success as the “battle of the laboratories” pitted US scientists against their Nazi counterparts in a race to develop the atomic bomb. Truman claims that the United States proved superior in this battle as it had in more traditional military endeavors. “We have spent two billion dollars on the greatest scientific gamble in history—and won,” he asserts, emphasizing the power of US industry and technology to overcome any obstacle.

From here Truman turns to a discussion of the nation’s plans for the new weapon. He makes plain to the nation and the world that another nuclear attack against the Japanese is likely. “Let there be no mistake; we shall completely destroy Japan’s power to make war.… They may expect a rain of ruin from the air, the like of which has never been seen on this earth.” He justifies the attack and states that Japanese leaders are to be held accountable for the destruction caused by the bomb because they could have accepted the earlier US demand for unconditional surrender and prevented the US attack. Atomic power, according to Truman, is a sign of US power and greatness and is a force that its opponents cannot possibly hope to resist.

The nuclear attack on Hiroshima did not force an immediate Japanese surrender. Two days later on August 8, the Soviet Union declared war on Japan and began an attack on Japanese-held Manchuria. The following day, Truman authorized a second nuclear attack, this time on the Japanese city of Nagasaki. Truman’s decision to drop atomic bombs on Hiroshima and Nagasaki had immense short- and long-term consequences. The nuclear blast in Hiroshima leveled more than four square miles of the city and immediately killed some 70,000 of the city’s estimated 300,000 to 350,000 combined civilian and military residents. Nagasaki lost about forty percent of its structures and suffered about 40,000 immediate casualties. Faced with the devastating realities of nuclear warfare and a Soviet onslaught from the west, the Japanese offered to surrender on August 10; the agreement was finalized and announced in early September. World War II was over, but the atomic age had just begun.

Although the US victory was welcomed, Truman’s decision was not without controversy. Some Americans—including scientists who had worked on the Manhattan Project and were aware of the bomb’s immense power—had opposed its use from the beginning. Truman declined to use an atomic weapon again, although the Japanese in requesting to keep the emperor as head of government had not given the United States the full and unconditional surrender that the Potsdam Declaration had demanded. Truman also refused to authorize its use in the Korean War, in which the United States was involved during Truman’s second term. Historians continue to debate Truman’s use of atomic weapons.

The threat of nuclear warfare hung over the nation for decades. The Soviet Union and other industrialized nations developed their own atomic technology during the late 1940s and 1950s, and Cold War tensions made the prospect of a nuclear exchange between the United States and Soviet Union seem likely. Truman’s successor, Dwight D. Eisenhower, supported a policy of mutually assured destruction and built up US nuclear reserves enough to ensure that the US response to a Soviet nuclear attack would be sufficient to completely destroy Soviet territories. In October 1962, the Cuban Missile Crisis placed the United States on the brink of a nuclear war, and nervous Americans tried to create survival plans in the event of attack. Nuclear disarmament and the end of the Cold War in the late twentieth century lessened such fears, but nuclear tests by hostile nations such as North Korea kept the atomic threat alive into the 2000s.

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