On August 6, 1945, at 8:15 a.m., the world’s first operational atomic bomb was dropped on Hiroshima, Japan. The bomb, nicknamed “Little Boy,” was delivered by the U.S. B-29 bomber Enola Gay, which flew from the American airbase on Tinian Island in the Pacific. The explosion released the equivalent force of over 12 kilotons of TNT, reducing around five square miles of the city to ashes and destroying over 60% of its buildings. Within four days, approximately 120,000 civilians had died, many of them instantly vaporized by the blast.
Three days later, on August 9, 1945, at around 11 a.m., another B-29 bomber from Tinian dropped the second atomic bomb on Nagasaki. This bomb, named “Fat Man,” caused similar devastation, obliterating about 2.5 square miles of the city and killing over 70,000 people instantly.
The decision to use these new weapons of mass destruction stemmed from the ongoing war in the Pacific, despite the end of the war in Europe in May 1945, following Adolf Hitler’s death and Germany’s unconditional surrender. The Allied forces, after the Normandy landings in June 1944 and the relentless advance of the Red Army on the Eastern Front, had crushed the German forces. However, the war against Japan continued, with American, British, and Commonwealth forces engaged in a brutal war of attrition across vast regions. Japanese forces fought with fanaticism, disregarding casualties on both sides.
Before the atomic bomb’s development, the Allies had planned for a conventional military defeat of Japan through Operation Downfall, which aimed to invade the Japanese home islands and force an unconditional surrender. Planners expected the operation to begin in November 1945 and last well into 1946. Operation Downfall was anticipated to be the largest military operation in history, surpassing even Operation Overlord. However, concerns about the likely heavy American and Allied casualties, as well as the potential impact on the approximately 100,000 Allied prisoners of war in Japanese hands, weighed heavily on decision-makers.
A smaller-scale preview of what Operation Downfall might entail was seen in the Battle of Okinawa from April to June 1945. Located just over 300 miles from mainland Japan, Okinawa was a critical staging post for any invasion force. The battle was marked by intense Japanese resistance, including mass kamikaze attacks that inflicted heavy casualties on American naval forces. The bloody and bitter fighting on Okinawa further fueled the desire for an alternative strategy to end the war.
The successful testing of the world’s first atomic bomb in the New Mexico desert on July 16, 1945, as part of the Manhattan Project, provided such an alternative. Initially motivated by the need to counter Nazi Germany’s atomic bomb project, the Manhattan Project had also considered Japan a potential target. The Allied leaders, having issued a warning to Japan at the Potsdam Conference, threatened “prompt and utter destruction” if Japan did not surrender unconditionally. However, Japan’s military hardliners refused to yield, leading to the decision to deploy the atomic bombs.
Hiroshima was chosen as the first target due to its significance as an economic and military hub that had been largely spared from air raids. When Japan still did not surrender after the bombing of Hiroshima, Nagasaki was selected as the second target. Even after this second catastrophic demonstration, it took almost another week before Japan finally accepted defeat. This decision was largely influenced by an unprecedented intervention from Emperor Hirohito, who compelled the military hardliners to surrender.
The use of atomic bombs ended World War II without further Allied military losses, but at a devastating cost to the Japanese civilian population. The bombings of Hiroshima and Nagasaki marked the beginning of a new era in warfare, introducing the specter of Mutually Assured Destruction that would dominate the Cold War. These bombings were essentially experiments in a new kind of warfare, the full implications of which were not fully understood at the time.
