Biggest US nuclear bomb dismantled
The last of America's biggest nuclear bombs, a Cold War relic 600 times more powerful than the one dropped on Hiroshima, was dismantled in what was called a milestone in President Barack Obama's mission to rid the world of the deadly weapons.
Workers in Texas separated the 300lbs of high explosives inside from the special nuclear material - uranium - known as the pit.
The work was done outside of public view for security reasons, but explosives from a bomb taken apart earlier were detonated as officials and reporters watched from less than a mile away.
Deputy secretary of energy Daniel Poneman called the disassembly "a milestone accomplishment". The completion of the dismantling programme is a year ahead of schedule, according to the US Department of Energy's National Nuclear Security Administration, and aligns with Mr Obama's goal of reducing the number of nuclear weapons.
Put into service in 1962, when Cold War tensions peaked during the Cuban Missile Crisis, the B53 weighed 10,000lbs and was the size of a minivan. Many of the bombs were disassembled in the 1980s, but a significant number remained in the US arsenal until they were retired from the stockpile in 1997.
The B53's disassembly ends the era of big megaton bombs, said Hans Kristensen, a spokesman for the Federation of American Scientists. The biggest nuclear bomb in the nation's arsenal now is the 1.2-megaton B83, he said. The B53 was nine megatons.
The 1.5-kiloton bomb dropped on Hiroshima, Japan, at the end of the Second World War killed as many as 140,000 people.
The B53s' size helped compensate for their lack of accuracy, Mr Kristensen said. Today's bombs are smaller but more precise, reducing the amount of collateral damage.
But Mr Kristensen said the Obama administration should not boast too much about dismantling the B53 when its arsenal of active nuclear warheads has been reduced by only 10 in the past seven months and Russia's arsenal has grown by 29. The two nations signed a treaty in December to reduce their arsenals.
Since the B53 was made using older technology by engineers who have since retired or died, developing a disassembly process took time. Engineers had to develop complex tools and new procedures to ensure safety.