The Way Forward on Missile Defense

Ballistic missile defenses have matured from a Cold War idea to a real-world necessity. Threats today from ballistic missiles are real, present and growing. Iran and North Korea have extensive inventories of these weapons that threaten their neighbors. Both are working on longer-range missiles capable of posing a direct danger to the United States in the coming years. Iran's continued pursuit of an illicit nuclear program and North Korea's rash intimidation after sinking a South Korean navy ship are but the most recent reminders of the real need for effective U.S. missile defenses.

To counter Iran's ballistic missile program, President Obama announced a phased adaptive approach for European missile defense last September -- a move unanimously welcomed by our NATO allies. The first phase begins next year with the deployment of radars and ship-based systems in southern Europe. Romania and Poland have agreed to host land-based defenses for the second and third phases.

A similar phased adaptive approach is being applied to missile defenses in the Middle East and East Asia. While the details of the deployments and host-country arrangements will differ by region, the common thread is significant improvement in ballistic missile defense capabilities, meant to protect our deployed forces overseas and our allies and partners.

In a departure from past approaches, we are no longer building systems anchored in one place and wedded to current threat assessments. We know that the capabilities of potential adversaries do not always progress according to intelligence assessments. Our program must adapt accordingly in the face of evolving and unpredictable threats.

We are also making continued progress in improving our ability to defend the U.S. homeland from ballistic missile attack. By the fall, the U.S. will have 30 deployed ground-based interceptors in Alaska and California, with eight more missile defense silos near completion.

The U.S. is committed to a "fly before you buy" approach supported by a rigorous and independently-monitored testing program. An essential element of that program, and a key capability for the phased adaptive approach, is the Standard Missile 3 (SM-3) interceptor. The SM-3 version deployed on Navy ships today has hit -- within inches -- its exact target in nine out of 10 tests. The accuracy of these tests has been confirmed in a variety of ways: by fiber-optic grids that can precisely indicate the point of impact on the target; by images taken from the interceptor in the very last moment before impact (images not available to the public for security reasons); by data from highly accurate radars and airborne sensors; and by extensive rocket sled tests and computer simulations on the ground. All these verification sources confirm that when a missile warhead was hit, it was destroyed. These results have been validated by an independent panel of experts with access to all of the classified and unclassified test data.

Missile defenses have become a topic of some discussion in the context of the Senate's consideration of the New START Treaty with Russia. The fact is that the treaty does not constrain the U.S. from testing, developing and deploying missile defenses. Nor does it prevent us from improving or expanding them. Nor does it raise the costs of doing so. We have made clear to our Russian counterparts that missile defense cooperation between us is in our mutual interest, and is not inconsistent with the need to deploy and improve our missile defense capabilities as threats arise.

U.S. ballistic missile defenses are effective, affordable and increasingly adaptable. These capabilities are critical to protecting U.S. citizens, our forces abroad, and our allies from real and growing threats.

Ms. Flournoy is the under secretary of Defense for Policy. Mr. Carter is the under secretary of Defense for Acquisition, Technology & Logistics.