Thursday 6 August 2020 marks 75 years since the catastrophic bombings of the Japanese cities of Hiroshima and Nagasaki, estimated to have claimed up to a quarter of a million civilians.
The bombings remain the only uses of nuclear weapons in armed conflict, marking pinnacle moments in history that altered the social and political character of the world and its popular culture.
Debate still swirls as to whether the bombings were ethical or legal.
Here's everything you need to know.
Who dropped the Hiroshima bomb?
It's worth remembering that while the bombings are often recalled in memory as a strictly American affair, the detonations were passed off by the UK.
Britain's blessing was required by the secret Quebec Agreement between the two countries that outlined terms for the coordinated development of nuclear weapons.
Why was Hiroshima bombed?
Ahead of the decisive nuclear bombings, the Allies (the UK, US, Soviet Union, and China) readied themselves for a more 'traditional' invasion of the Japanese mainland in the final year of the Second World War.
The war in Europe had ended three months earlier with Germany signing its surrender on 8 May 1945; now the Allies were turning their attention to the remaining Pacific conflicts.
This invasion was to have been a logistically mammoth undertaking, costly in both resources and the potential for loss of personnel.
A 'conventional' firebombing campaign made use of jellied petroleum and severely damaged Japanese cities, including the capital Tokyo, which was rendered almost unrecognisable by the Allies' destruction.
The Allies issued an ultimatum in the form of the Potsdam Declaration, which called for the unconditional surrender of the Imperial Japanese armed forces.
Should they refuse they would face "prompt and utter destruction."
What happened at Hiroshima?
The Manhattan Project - a research and development project undertaken between the US, Britain and Canada - had at this point developed two types of atomic bomb, and it was ordered that these bombs should be used against key Japanese cities.
On Monday 6 August 1945, a modified B-29 Superfortress (the US’ Enola Gay) heavy bomber dropped the uranium bomb "Little Boy" on Hiroshima.
Though Hiroshima was militarily significant on account of its notable military garrison, most of the dead in the instantly devastated city were civilians.
Three days later, another B-29 dropped a plutonium implosion bomb called "Fat Man" on Nagasaki in Japan's south.
What was the effect of the bombings?
It is estimated that up to 226,000 people died as an effect of the blasts, though only about half of those deaths occurred on the days of the bombings.
For months afterwards, people continued to die from the effects of burns, injury and radiation sickness.
Japan surrendered six days after the bombing of Nagasaki on 15 August 1945, a move which effectively ended World War II.
In the UK, 15 August is known as Victory in Japan Day (VJ Day).
Why did Japan attack Pearl Harbour and join WW2?
On the morning of 7 December 1941, Japanese bombers, fighters and torpedo planes attacked the American naval base at Pearl Harbour on Oahu Island, Hawaii.
This surprise attack brought the United States into the Second World War and changed the course of history.
The attack was the climax to a decade of deteriorating relations between the United States and an aggressively expansionist Japan.
Japan’s invasion of China in 1937, its subsequent alliance with Germany and Italy in 1940, and its occupation of French Indo-China in July 1941, prompted the United States to sever practically all commercial and financial relations with Japan.
Though Japan continued to negotiate with the United States up to the day of the Pearl Harbor attack, the government of Prime Minister Tojo Hideki had decided on war.
Admiral Yamamoto Isoroku, the commander-in-chief of Japan’s Combined Fleet, had planned the attack against the US Pacific Fleet with great care.
Yamamoto had opposed war with the United States because he feared Japan would lose a protracted struggle with such a powerful opponent.
However, once the decision to go to war was made, Yamamoto argued that Japan’s only chance for victory lay in a surprise attack that would cripple the American naval forces in the Pacific.
Until the Japanese attack on Pearl Harbour American public opinion was overwhelmingly hostile to entering the war.
The attack on Pearl Harbour transformed the public mood and swept away hitherto strong support for American neutrality; on December 8, congress declared war on Japan with only one dissenting vote.
Less than six months after the attack, the United States Pacific Fleet was able to inflict a devastating blow on the Japanese navy and air force at the battle of Midway Island.