Iran is nuclear capable. If Iran's leaders decided they wanted a nuclear bomb, they could build one. They have the material, the technical ability, and likely have a design. They have had these capabilities for at least five years, when they accumulated enough raw material that could be converted into the core of a bomb.
But Iran does not have a bomb now. U.S. intelligence officials have high confidence that Iranian leaders have not made the decision to build a bomb. There is much confusion -- some of it intentionally spread -- about how long it would take Iran to build a weapon.
An outstanding team of seasoned national security experts has just published a clear, detailed explanation of Iran's nuclear timeline. The report of the Iran Project was endorsed by 34 security leaders, including Brent Scowcroft, Sam Nunn, Gen. Tony Zinni, Adm. James Fallon, Gen. Frank Kearney, Carla Hills, Anne Marie Slaughter, Chuck Hagel, Adm. Joe Sestak, Jessica Mathews, Zbigniew Brezinski, Nicholas Burns and this author.
Here is an excerpt from the report (on p. 22) that provides a sound basis for debating what actions should be taken to convince Iran not to build nuclear weapons. This report is intentionally conservative. There may be serious technical problems that make the timeline much longer. I have highlighted in bold key phrases.
While there are differences of opinion on this issue, we believe it would be extremely difficult for Iran to hide a nuclear program devoted to weapons development. No monitoring and detection system is failure-proof, but Iran has little reason to be confident that it could get away with creating a secret program to produce fissile material for a weapon.
Were Iran to attempt to produce a single bomb's worth of highly enriched uranium (HEU), it would take at least one month (although some experts believe the timeline could be as long as four months or more). It is important to note that while the ability to build a single bomb is a somewhat useful theoretical construct, it has little or no correspondence to how nuclear weapons programs function in the real world.
Historically, no country in the nuclear age has sought as its goal to build one nuclear weapon; nor has any country adopted a strategy of building one weapon knowing that as a consequence, its program would be exposed. The timeline for producing a single bomb's worth of HEU is subject to change, depending on the number and type of operational centrifuges available as well as the size of Iran's stockpile of already enriched uranium, particularly 20% enriched uranium. Conservatively, it would take Iran a year or more to build a military-grade weapon, with at least two years or more required to create a nuclear warhead that would be reliably deliverable by a missile.
In short, it is likely that the United States would receive some warning and have at least a month to make a decision on action -- military or other. Understanding the difference between the one-month timeline of producing sufficient fissile material in order to produce a weapon, and the two-year timeline of creating a nuclear warhead, is critical when considering the likely success of military action.
After a month, the weapons-grade uranium (WGU) could be reduced significantly in size (25 kilograms); if properly encased, it could be easily hidden and would be highly mobile. This would be a very hard target to detect and destroy. While it would take some additional time for Iran to translate the WGU into a meaningful military capability, the ability for the United States or others to launch preventive military strikes would be reduced. In contrast, the facility used to enrich the WGU is immobile and large and therefore an easier and somewhat vulnerable target (unless deeply buried).
...The more apparent the decision to make a weapon, the more persuasive the justification for military action would be to the international community, including the United Nations Security Council. While Israel's more limited military capabilities and earlier "red line" create a closing window of opportunity to take military action, the U.S. could afford to wait for its red line to be crossed -- Iran undertaking a dedicated weapons program -- before deciding whether to take preventive military action.
...Given the deepening mutual distrust between the U.S. and Iran; congressional sympathy for Israel's perspective on a nuclear-capable Iran; and the conviction among some parties that Iran has already secretly decided to build a nuclear weapon, we believe the most likely military scenario is one in which preemptive, unilateral action against Iran is initiated by the U.S. and/or Israel, under conditions of some uncertainty about Iran's real intentions. That scenario is the primary focus of our paper.