This week marks the 10th anniversary of the first operational deployment of the Ground-Based Midcourse Defense (GMD) system, the only ballistic missile defense system that currently protects the U.S. from a long-range ballistic missile threat. The interest in the development and deployment of the system came after the U.S. withdrew from the Anti-Ballistic Missile Treaty in 2001. The Treaty gave U.S. adversaries a free hand to attack U.S. citizens for almost 30 years.

U.S. adversaries took advantage of U.S. vulnerability. Ballistic missiles spread after the end of the Cold War. North Korea and Iran have started long-range ballistic missile programs, often with help of the scientists from the former Soviet bloc and China. Both countries have also pursued nuclear weapons programs, and North Korea successfully detonated nuclear devices in 2006, 2009, and 2013.

Ballistic missile defense is one of the most technologically difficult feats a nation can accomplish. The U.S. developed hit-to-kill technology, which means that an interceptor positions itself in the path of an incoming enemy missile and destroys it by the sheer force of an impact in several kilometers-per-second speeds. Some even thought this impossible several years ago. The U.S. does not use nuclear interceptors.

Today, the GMD system is operationally deployed. If North Korea decides to launch a ballistic missile, the President will be able to deploy one of four interceptors in California or 26 in Alaska. Under some circumstance, the President will even have an option to launch a second round of interceptors if the first one misses. The system had a successful intercept earlier this year. The test was the most challenging to date and involved a successful discrimination of countermeasures.

The U.S. needs to get ahead of the ballistic missile threat and continue to improve the GMD system. Its adversaries are not timid. In addition, the U.S. needs to continue to develop and deploy a layered ballistic missile defense system, including space-based interceptors. Washington must improve the sea-based Aegis Standard Missile-3 system and continue to deploy the European Phased Adaptive Approach.