The last of America's most powerful Cold War-era nuclear bombs - the B53 - has been dismantled in Texas.
Experts have separated around 300lb (136kg) of high explosives from the bomb's uranium "pit".
Weighing 10,000lb, the B53 was the size of a minivan and said to be 600 times more destructive than the atomic bomb dropped on Hiroshima, Japan, in 1945.
It was first put into service at the height of the Cold War in 1962, and remained in the US arsenal until 1997.
The bomb was designed to hit targets deep underground, such as bunkers in which military and civilian leaders might be sheltering.
Carried by B-52 bombers, the "bunker busters" used five parachutes to land softly on their targets before detonating a nine megaton explosion, in effect simulating an earthquake.
They have been superseded by bombs that burrow into the ground and then explode.
The first B53s were destroyed in the 1980s but several remained in service until 1997, when they were all retired.
A dismantling programme had to be specially designed for the B53s, which were made with older technology and by scientists who have since retired or died.
The US Department of Energy's National Nuclear Security Administration (NNSA) has said the programme, which was completed once this final bomb had been dismantled, is a year ahead of schedule.
The head of the NNSA, Thomas D'Agostino, called the decommissioning of the last B53 a "significant milestone".
"The world is a safer place with this dismantlement," he said.
"The B53 was a weapon developed in another time for a different world. Today, we're moving beyond the Cold War nuclear weapons complex that built it toward a 21st Century nuclear security enterprise."
After disassembly, the uranium pits from the bomb will be temporarily stored at the Pantex plant near Amarillo, Texas, where Tuesday's dismantling was carried out.
The plant is the only nuclear weapons assembly and disassembly facility in the US.
The plant is likely to be involved with future disassembly projects as older weapons are retired.
According to figures released by the US state department in May 2011, the US has 5,113 nuclear warheads in its current stockpile, down from 31,255 in 1967.