On
6 August 1945, the US attacked the Japanese city of Hiroshima with an
atomic bomb in a bid to end the second world war. Seventy years after
the devastating power of nuclear weapons was first demonstrated, nine
states retain them in their arsenals
The Manhattan Project
US atomic weapons research began after nuclear fission
was discovered by German scientists in 1938, prompting fears of a Nazi
bomb. After Japan attacked Pearl Harbor in 1941, work centred on the
Manhattan Project, led by Robert Oppenheimer at Los Alamos in New
Mexico. Germany had already surrendered when the first nuclear weapon
test took place on 16 July 1945, but war in the Pacific continued.
The attacks
After the successful test US president Harry Truman
authorised the use of two weapons against Japan, arguing it would be a
quicker and less bloody way to secure surrender than an invasion. There
was no capitulation after the first bomb, codenamed Little Boy,
destroyed more than 10 sq km of Hiroshima on 6 August 1945. Three days
later the more powerful Fat Man device hit Nagasaki.
The casualties
Estimates of people killed in the immediate aftermath of
the two bombings and the months that followed range as high as 246,000.
Many of the survivors suffered horrific burns and the enduring effects
of radiation illnesses. With more attacks planned by the US, Japan
surrendered on 15 August.
Cold war follows world war
The USSR, which had spies in the Manhattan project,
tested its first nuclear bomb in 1949. Increasingly powerful
thermonuclear devices were tested in remote parts of the world,
culminating with the Soviet Tsar Bomba which produced an explosion
visible 1,000 kilometres away and a mushroom cloud taller than Everest.
Mutually assured destruction
Throughout the 1960s, the superpowers developed huge
arsenals. According to the doctrine of mutually assured destruction
(MAD), this made nuclear war unlikely as neither side could ever
eliminate the other’s ability to retaliate. The 1970 non-proliferation
treaty was designed to restrict the capability to existing nuclear
powers and enshrine a commitment to disarmament, but other states were
already pursuing their own programs.
Disarmament delayed
The collapse of the Soviet Union in 1991 removed the
cold war's uneasy certainty. There are now nine known nuclear powers,
chief among them the US and Russia, which retain formidable stockpiles
even after substantial disarmament. Only South Africa has ever developed
and then relinquished nuclear weapons. Ukraine surrendered its
Soviet-era weapons in 1994 in exchange for a guarantee of its
territorial integrity.
The doomsday clock
Since 1947, the Bulletin of the Atomic Scientists has
been publishing a yearly assessment of the risk of global catastrophe in
the form of a clock counting down to midnight. In 2015, with climate
change now included as a risk, it stands at three minutes to midnight,
as existing powers upgrade their arsenals. Ongoing risks to humanity
include further proliferation, a nuclear terrorist attack and the
problem of radioactive waste.
