Engineers at the United States' nuclear weapons lab in Albuquerque, New Mexico, have spent the past few years designing and testing the B61-12, a high-tech addition to our nation's atomic arsenal. Unlike the free-fall gravity bombs it will replace, the B61-12 is a guided nuclear bomb. A new tail kit assembly, made by Boeing, enables the bomb to hit targets far more precisely than its predecessors. Greg Maxon Using "Dial-a-yield" technology, the bomb's explosive force can be adjusted before launch from a high of 50,000 tons of TNT equivalent to a low of 300 tons—that's 98 percent smaller than the bomb dropped on Hiroshima 70 years ago. Despite these innovations, the government doesn't consider the B61-12 to be a new weapon but simply an upgrade.