In the Cold War arms race, scientists rushed to build thousands of warheads to counter the Soviet Union. Today, those scientists are racing once again, but this time to rebuild an aging nuclear stockpile.
Scientists at Los Alamos National Laboratory in New Mexico are locked in an intense competition with rivals at Lawrence Livermore National Laboratory in the Bay Area to design the nation's first new nuclear bomb in two decades.
The two labs have fiercely competed in the bomb trade with technologies as disparate as Microsoft's and Apple's.
The new weapon, under development for about a year, is designed to ensure long-term reliability of the nation's inventory of bombs. Program backers say that with greater confidence in the quality of its weapons, the nation could draw down its stockpile, estimated at about 6,000 warheads.
Scientists also intend for the new weapons to be less vulnerable to accidental detonation and to be so secure that any stolen or lost weapon would be unusable.
By law, the new weapons would pack the same explosive power as existing warheads and be suitable only for the same kinds of military targets as those of the weapons they replace. Unlike past proposals for new atomic weapons, the project has captured bipartisan support in Congress.
But some veterans of nuclear arms development are strongly opposed, contending that building new weapons could trigger another arms race with Russia and China, as well as undermine arguments to stop nuclear developments in Iran, North Korea and elsewhere.
And, the critics say, It would eventually increase pressure to resume underground nuclear testing, which the U.S. halted 14 years ago.
Inside the labs, however, emotions and enthusiasm for the new designs are running high.
"I have had people working nights and weekends," said Joseph Martz, head of the Los Alamos design team. "I have to tell them to go home. I can't keep them out of the office. This is a chance to exercise skills that we have not had a chance to use for 20 years."
A thousand miles away at Livermore, Bruce Goodwin, associate director for nuclear weapons, described a similar picture: The lab is running supercomputer simulations around the clock, and teams of scientific experts working on all phases of the project "are extremely excited."
The program to build the new bomb, known as the "reliable replacement warhead," was approved by Congress in 2005 as part of a defense spending bill. The design work is being supervised by the National Nuclear Security Administration, which is part of the Energy Department.
The laboratories submitted detailed design proposals in March that ran more than 1,000 pages each to the Nuclear Weapons Council, the secretive federal panel that oversees the nation's nuclear weapons. A winner will be declared this year.
If the program is implemented, it would require an expensive remobilization of the nation's nuclear weapons complex, creating a capacity to turn out bombs at the rate of three or more a week.
Proponents of the project foresee a time when nuclear deterrence will increasingly rest on the nation's capacity to build new bombs, rather than on maintaining a massive stockpile.
The proposal comes as Russia and the United States have agreed to further reduce nuclear stockpiles. The Moscow Treaty signed in 2002 by President Bush and Russian President Vladimir V. Putin calls for each country to cut inventories to between 1,700 and 2,200 warheads by 2012.
Without the reliable replacement warhead, U.S. scientists say the nation will end up with old and potentially unreliable bombs within the next 15 years, allowing adversaries to challenge U.S. supremacy and erode the nation's so-called strategic deterrent.
The new bomb "is one way of ensuring that our capability is second to none," said Paul Hommert, a physicist who heads X Division, the Los Alamos unit that built the first atomic bomb during World War II. "Not only today, but in 2025."
But critics say the program could plant the seeds of a new arms race.
The existing stockpile will be safe and reliable for decades to come, according to defense experts and nuclear scientists who have long supported strategic weapons. They say that rather than making the nation safer, the program will squander resources, broadcast the message that arms control is dead and even undermine the reliability of U.S. weapons.
The new bomb would have to be built and deployed without testing. The U.S. last conducted an underground test in Nevada in 1992 and has since imposed a moratorium on new testing.
But without a single test, doubts about the new bomb's reliability would eventually grow, said Sidney Drell, former director of Stanford University's Linear Accelerator Center and a longtime advisor to the Energy Department.