"It took about 45 seconds from when the bomb left the aeroplane until the explosion. And I think there wasn't a man in the aeroplane who wasn't timing it with his watch or counting, or doing something" - Enola Gay crewman, Theodore Van Kirk
On August 6, 1945, the full horrors of atomic warfare, which can be traced back in fiction as early as 1895, were fully realised in Hiroshima, Japan.
On that day, the bomb codenamed 'Little Boy' (pictured top right) was dropped on the city by the United States B-29 flying "Superfortress" Enola Gay, which happened to be named after the pilot's mother.
At that time, anti-Japanese propaganda - later described as "annihilationist and exterminationalist rhetoric" by the UK embassy in Washington - was tolerated at all levels of US Society.
And while these anti-Japanese sentiments grew, so too did the US's weapons capability - the seeds of which had been sewn in a 1939 in the form of a letter signed by Albert Einstein to US President Franklin D Roosevelt which urged the beginning of an atomic weapons research program.
The Manhattan Project, and the £15,000 collectible bomb part
Behind the Little Boy bomb was a $23bn (in today's money) top secret weapons program known as the Manhattan Project, led by the United States with the aid of Canada and the United Kingdom.
It was perhaps the greatest secret project of the 20th century, whose roots lay in fears since the 1930s that Nazi Germany was investigating a nuclear weapons program of its own.
Such fears were confirmed by Einstein, who later wrote of his 1939 letter to Roosevelt:
"Because of the danger that Hitler might be the first to have the bomb, I signed a letter to the President... Had I known that the fear was not justified, I would not have participated in opening this Pandora's box... For my distrust of governments was not limited to Germany" - Albert Einstein
Following the 1945 bombings of Hiroshima and Nagasaki, to commemorate their work in producing three successful nuclear explosions (including a test) souvenirs were taken by, or presented to, the 13,000 consultants and scientists behind the Manhattan Project.
Years later, in 2009, one of those souvenirs emerged on the collectors' markets: a 160mm diameter spare Ball race from the construction of the 'Little Boy' bomb from the collection of the late Professor Samuel Eilenberg, Professor of Mathematics at Columbia University in WW2.
This spare part from the Hiroshima
According to experts, the Ball race - 64 years old and one of only two known - was central to the construction of 'Little Boy'. It appeared on the market priced £15,000.
The bomb that 'ended World War Two'
Just three days after the Enola Gay's mission, the US detonated the "Fat Man" bomb over Nagasaki on August 9. The second atomic bomb ever to be used as a weapon, it was detonated at an altitude of about 1,800 ft (or 550m) over the city by the B-29 bomber Bockscar.
Just as the Enola Gay had listed Nagasaki as a 'back up' target during its mission, Fat Man had actually been destined for the city of Kokura. But because of obscuring clouds above Kokura, the 'back up' city was this time chosen.
Today, the Bockscar - also referred to as "the plane that ended World War Two" - is on permanent display at the National Museum of the United States Air Force, Dayton, Ohio.
And, as with letters written by Einstein about the use of atomic weaponry, memorabilia from the Enola Gay and Bockscar missions have also traded hands on the collectors' markets. Among them was a signed 10 x 8 photograph signed by the crew of the Bockscar, sold by Paul Fraser Collectibles earlier this year.
Also on the market is a black and white photograph of the Enola Gay bearing an autograph and inscription by two of its crew: "Robert Lewis Co-Pilot 'Enola Gay' Tinian Runway Aug 6 1945" and "Thomas W. Ferebee - Bombardier - Enola - Gay - Aug 6 1945."
These memorabilia items may recall one of the most horrific episodes in human history, but they are also essential reminders of one of the darker episodes of World War II - the destructive excesses of which will hopefully never be seen again.
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