On 9 August 1945 the US dropped a second atomic bomb “Fat Man” on Nagasaki, Japan, destroying part of the city.

The Fat Man weapon, containing a core of about 5 kg (11 lb) of plutonium, was dropped over the city’s industrial valley. It exploded 47 seconds later at 11:02 at 503 ± 10 m (1,650 ± 33 ft), above a tennis court, halfway between the Mitsubishi Steel and Arms Works in the south and the Nagasaki Arsenal in the north, nearly 3 km (1.9 mi) northwest of the planned hypocenter. 

The blast was confined to the Urakami Valley, and a major portion of the city was protected by the intervening hills. The resulting explosion released the equivalent energy of 21 ± 2 kt (87.9 ± 8.4 TJ).

Of 7,500 Japanese employees who worked inside the Mitsubishi Munitions plant, including “mobilized” students and regular workers, 6,200 were killed. Some 17,000–22,000 others who worked in other war plants and factories in the city died as well. The 1946 Manhattan Project report estimated 39,000 dead and 25,000 injured, and the 1951 U.S.-led Joint Commission report estimated 39,214 dead and 25,153 injured; Japanese-led reconsiderations in the 1970s estimated 70,000 dead in Nagasaki by the end of the year.  A modern estimate by the Radiation Effects Research Foundation (RERF) estimates a city population of 250,000 to 270,000 at the time of the bombing, of which 60,000 to 80,000 died by the end of the year.

At least eight Allied prisoners of war (POWs)—British Royal Air Force Corporal Ronald Shaw, and seven Dutch POWs—were killed, and as many as thirteen may have died.  American POW Joe Kieyoomia survived, reportedly having been shielded from the effects of the bomb by the concrete walls of his cell.  The 24 Australian POWs in Nagasaki survived.