In each city, those closest to ground zero – known as the hypocentre of the explosion – stood little chance of survival. Almost everyone within a radius of 1.2 kilometres and unshielded from the bomb’s effects died instantly or within a few weeks.

Ground temperatures at the hypocentre reached 3,000 to 4,000 degrees Celsius, with people as far away as 3.5 kilometres suffering burns. Powerful shock waves destroyed most wooden structures within 2 kilometres.

Even at a distance of 1 kilometre, people received a high enough dose of ionising radiation to die from acute radiation poisoning. Many people much further away also died from the delayed effects of radiation exposure.