It's harder -- and more time-consuming -- than you'd think.
Today, U.S. President Barack Obama signs into law the next round of unilateral sanctions taking aim at Iran's energy sector. With this bill, Washington is seeking to stem what many view as Tehran's imminent nuclear future. But how imminent is that future, exactly?
Some would say it is very imminent. On June 27, CIA Director Leon Panetta estimated that it would take Iran approximately two years to build a nuclear bomb if it made the decision to do so. The Wall Street Journal seized on his statement, warning hysterically on June 29 that "Iran stands barely two years from an atomic bomb that could target Israel, Europe and beyond."
Pundits, too, have consistently claimed that Iran is just around the corner from acquiring nukes. Washington Post columnist Charles Krauthammer, for example, urgently warned in July 2004, "Iran will go nuclear during the next presidential term." In January 2006, he claimed, "Iran is probably just months away." A few months later, in September, when no bomb appeared, he wrote, "The decision is no more than a year away." William Kristol, Niall Ferguson, and John Bolton, among others, have made similar claims -- and been similarly proved wrong by the passage of time.
In fact, it is much harder to build a deliverable weapon than most pundits assume. Panetta's estimate leans toward the worst-case scenario, in which the weapons-building process proceeds perfectly smoothly. But the best expert assessments indicate that it would actually take Iran about three to five years to develop a nuclear bomb. Here's how that process would probably unfold -- and the reasons why it's not likely to happen in the timeline the doomsayers would have you believe.
Step 1: The Decision
Iran is certainly moving to acquire the technology that would enable it to make a weapon. But, as a 2009 Joint Threat Assessment by the EastWest Institute concludes, "[I]t is not clear whether [Iran] has taken the decision to produce nuclear weapons. "The regime must weigh the political and security costs of developing nuclear weapons before moving ahead. And Iran might decide, like Japan, that its needs are best served by approaching the threshold of building a bomb (acquiring the technical capability and know-how) but not actually crossing the line and risking an arms race among its rivals or a pre-emptive attack from the United States or Israel.
"Nobody knows if Iran has taken this decision," Sharon Squassoni, director of the Proliferation Prevention Program at the Center for Strategic and International Studies, told Agence France-Press on June 28. "It's more in their interest to have this ambiguity."
Step Two: The Right Stuff
Should Iran decide to proceed, it must accumulate a sufficient quantity of the indispensable component for the core of the bomb -- highly enriched uranium (HEU) or plutonium. Iran is pursuing production paths for both, though its uranium enrichment capabilities are years ahead of its plutonium reprocessing plans.
There are two ways for Iran to produce HEU, uranium that includes 90 percent of the isotope U-235. Using its centrifuges at the Natanz facility, it could take natural uranium, composed of 0.07 percent U-235, and steadily enrich it to weapons-grade material. This would be a flagrant violation of its obligations under the Nuclear Non-Proliferation Treaty (NPT). If Iran chose this route, it would have to withdraw from the treaty and kick out international inspectors. Running full tilt at Natanz, it then would take Iran about one year to enrich enough uranium for one bomb.
More likely, Iran could continue its current path of increasing its stockpile of low-enriched uranium (3 percent U-235), which it claims is for peaceful purposes. At some point, Iran could then leave the NPT, kick out the inspectors, and pump the uranium back through the centrifuges to enrich it to higher levels. The Joint Threat Assessment estimates this path could produce one bomb's worth of HEU within three to six months. Panetta seemed to say that, using this method, Iran could have enough HEU to construct two bombs in one year.
Still, recent technological difficulties could prolong the process: In February, the Washington-based Institute for Science and International Security reported that the number of working Iranian centrifuges, the machines that enrich uranium, had decreased since mid-2009. Although Iran continues to install centrifuges, it operates nearly 1,000 fewer centrifuges than it did in May 2009.
Recently, Iran has enriched uranium to about 20 percent, purportedly as fuel for its research reactor. If Iran accumulated enough 20 percent-enriched uranium -- it had 11 kilograms at the end of May -- and used this as source material, it could produce weapon-quality HEU even more quickly.
In all cases, it would take Iran an additional six months to convert the HEU from its current gaseous form into metal for a bomb.
Step 3: The Gadget
The technical path to a bomb does not end with HEU. To produce a crude nuclear device would take an additional year, assuming Iran has a workable design and the components to build it. But the leap to a sophisticated nuclear warhead, one that could be used as a weapon, could take an additional two to five years. During this period, Iran would need to manufacture the nonnuclear components, test and refine them, and ultimately, conduct one or more nuclear explosive tests. Troubleshooting the nonnuclear components might go undetected, but global monitors would detect any nuclear test explosion, surely leading to increased pressure on Iran.
Vice chairman of the Joint Chiefs of Staff, Gen. James Cartwright, confirmed this timeline before the Senate Armed Services Committee on April 14. He said a "deliverable weapon that is usable tactically" would take "another two to three, potentially out to five years."
Step 4: Honey, I Shrunk the Warhead
Iran could make a very heavy crude nuclear device, deliverable by truck, approximately one year after it produced the HEU. But this heavier device, though useful as a weapon, would be too large to deliver on Iran's planes or missiles, which can't carry a weapon that weighs over 1,000 kilograms. A smaller, more sophisticated weapon is needed if Iran is to develop a credible nuclear deterrent -- and shrinking a nuclear warhead doesn't happen overnight. Retired U.S. Gen. Eugene Habiger says that "the miniaturization of a nuclear warhead is probably the most significant challenge that any proliferant would have to face." Habiger noted:
The first U.S. ICBM's [intercontinental ballistic missiles], the warheads on those ICBM's, were in the 4,000-5,000 kg range. That's the best we could come up with when we first started ... Only after six to eight years, of very intensive engineering development and aggressive testing, did we get down to 1,000 kg.
Step 5: Deliverance
Iran would also have to develop a re-entry vehicle for its weapon. A ballistic missile follows a parabolic trajectory, shooting up through the atmosphere, traveling a short distance through outer space, and re-entering the atmosphere to strike its target. The warhead must be sturdy enough to survive the extreme conditions it encounters along this flight path, and developing this technology is no small task. It is one thing to test a nuclear weapon in carefully controlled conditions. It is another to build a weapon that can withstand the fierce vibrations, G-forces, and high temperatures of launch and re-entry into the atmosphere. Iran has not demonstrated the capability to build such a re-entry vehicle thus far.
Step 6: Range Matters
Today, Iran's ballistic missiles can reach targets no more than 1,600 kilometers from Iran's borders, carrying bombs that weigh no more than 750 kilograms. That's barely enough range to hit even Iran's closest neighbors.
A new report by the International Institute for Strategic Studies concludes that Iran won't be able to field long-range missiles capable of hitting Western Europe, approximately 3,700 kilometers away, before 2014 or 2015. The report also extends the timeline for an Iranian ICBM, suggesting that Tehran must first field an intermediate-range missile before embarking on a program that could develop a missile capable of striking the United States, which is 9,000 kilometers away. Thus, the report concludes that an Iranian ICBM "is more than a decade away from development."
Iran could accelerate this timeline if it received foreign assistance. An April report by the Pentagon on Iran's military potential estimated that with foreign assistance, Iran could develop an ICBM capable of reaching the United States by 2015. However, continued efforts to isolate Iran and work with key states, including Russia and China, to restrict of the spread of nuclear and missile-related technologies help reduce the likelihood of this assistance.
* * *
With Iran's nuclear timeline so fluid, it's crucial not to react in a panicked way based on a false sense of urgency. A military response in particular could have grave consequences, while doing nothing to provide a long-term solution to the problem. "[T]here is no military option that does anything more than buy time," said Defense Secretary Robert Gates in September 2009. "The estimates are [that a strike on Iran's nuclear facilities delay it] one to three years or so."
Chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, also warned on June 28 that a military strike on Iran would be "incredibly destabilizing" to the region. It would likely increase support for the Iranian regime, Mullen noted earlier, even among Iran's Green Movement.
So the next time you hear a pundit claiming that Iran is on the verge of attaining nuclear weapons, don't panic. Like the boy who cried wolf, those pundits might eventually be right. For now, however, Iran has a ways to go -- and keeping that in mind is the best way to develop a measured response to the Islamic Republic's nuclear ambitions.
Shannon Stapleton-Pool/Getty Images