Play the Interceptor,
Or Work with the Real Thing. 

Intercept and eliminate incoming warheads by using your mouse to target them, then click to launch your missiles. As you gain experience and points, you will have access to MDA's Multiple Kill Vehicle (MKV), which allows you to destroy multiple enemy warheads simultaneously. To select the MKV, click on its icon in the lower right of the screen or tap the space bar. 

To win ­survive four 1-minute, progressively more difficult levels. If you sustain, 40 enemy hits, your cities are destroyed and the game is complete. 

Lead the greatest technological achievement of our time. 

U.S. Missile Defense Agency.