Building up U.S. missile defense capabilities could deter Iranian aggression and dissuade them from further improvements

While Pattani and others suggest that the United States can wait to make some of the above investments until “intelligence estimates shift or it otherwise becomes clear that Iran is developing nuclear weapons,” there are several real benefits to committing to a credible BMD architecture today.³³ The first and most obvious is that investments now are necessary to have a credible ballistic missile defense architecture in place that would be able to counter threats from a nuclear-armed Iran. In addition to being able to destroy an Iranian missile that has been launched, missile defenses would aid in U.S. attempts to deter Iranian aggression in the first place. These defenses need not be infallible; they just need to make “the expected costs of aggression high and the expected probability of achieving the benefits low.”[footnote=3074]³⁴[/footnote=3074]

Being prepared in the near term to counter Iranian threats in the future would also help complicate Tehran’s current nuclear weapons decisionmaking calculus. Missile defense calls into question Iran’s most likely delivery system for a nuclear weapon, and decreasing the likelihood of a successful attack calls into question the viability of the potential threat of a nuclear strike. Proactive action on BMD today introduces uncertainty into Iran’s planning as it considers the utility of building nuclear weapons or developing ICBMs. Patrick Disney argues, “The more the U.S. does to prepare for the day after Iran obtains a nuclear weapon, the greater Iran’s incentive becomes to acquire a nuclear deterrent of its own.”³⁵ However, a purely defensive BMD capability overcomes this problem. If the most obvious use for a nuclear weapon is no longer certain to be available, the costs of acquisition become less tenable.