A U.S.-made nuclear bomb that is 600 times more powerful than the atomic bomb dropped in Hiroshima during World War II was dismantled in Texas on Tuesday.

The 9-megaton B53, which weighs 4,500 kilograms and is the size of a minivan, is the last of its kind to be disassembled. Built in 1962 at the height of the Cold War, the bomb had been retired since 1997. Its dismantling is in line with U.S. President Barack Obama's goals of reducing the U.S. nuclear stockpile.

The engineers who built the bomb are already dead leaving no one with the competency and knowhow to dismantle it. It took engineers of the U.S. Department of Energy's National Nuclear Security Administration time to do so because a new and safe disassembly process and tools had to be developed.

"We knew going in that this was going to be a challenging project, and we put together an outstanding team with all of our partners to develop a way to achieve this objective safely and efficiently," said John Woolery, general manager of the Pantex Plant, where the B53 was kept and dismantled, according to the Associated Press. The plant is near Amarillo, Texas.

The engineers separated 135 kilograms of high explosives from the uranium pit to complete the dismantling, according to Pantex spokesman Greg Cunningham.

The B53 was designed to destroy underground targets. A B-52 bomber can carry and launch it. Many such bombs were dismantled in the 1980s with the remaining retired in 1997.

While the B53 is gone, the U.S. still has a powerful nuclear bomb in its arsenal, the B83 which is 1.2 megatons.