Iranian Missile Defense... What Missile Defense...

Missile defense will be strategically useless against the nuclear threats from Iran -- or anywhere else.

Barack Obama's administration has characterized its new missile defense plan as a more judicious alternative to George W. Bush's expensive (but untested) Eastern European-based interceptor system. Writing in the Financial Times last month, Secretary of State Hillary Clinton called it "a stronger and smarter approach than the previous program," noting it will be deployed faster and less expensively, so as "not [to] waste time or taxpayer money." That may sound like a winning combination, but in reality, the main difference between the old and new plans is that the latter doesn't step on Russia's toes. Otherwise, it will be just as strategically ineffective as the original.

Speaking broadly, missile defense comes in two different flavors. The first is tactical missile defense, such as the U.S. Patriot system, which protects a theater of battle against short-range conventional rockets. The second category is strategic, or national, missile defense: systems meant to guard against adversaries' nuclear-tipped missiles. While the first of these types is conceptually sensible, the second is not and may even make the world a more dangerous place.

The reason for this is quite simple. A 70 percent effective tactical missile defense (to pick an optimistic number) makes a lot of sense. If 10 conventional missiles are headed your way, stopping seven is undeniably a good thing. Stopping seven of 10 nuclear warheads, however, is less decisive since even one will visit unacceptable devastation upon the United States. Just one nuclear-tipped missile penetrating your missile shield is about the equivalent of a million conventional missiles making it through.

So even after the United States has set up and activated a national missile-defense system, it still will not have neutralized the perceived threat from Iran. Not only that, but Washington's strategic calculations toward Tehran will remain unaffected: The United States will still need to be just as worried about Iran's missiles, since the destruction of even one U.S. city or region is simply too high a cost to bear. For that security equation to change, national missile defense would need to intercept 100 percent of incoming nuclear warheads -- an unattainable goal for any piece of machinery.