What is GMD?

GMD most likely refers to Ground-based Midcourse Defense, a component of the U.S. Ballistic Missile Defense System (BMDS). It is designed to intercept incoming intercontinental ballistic missiles (ICBMs) in the midcourse phase of their trajectory, which is outside the Earth's atmosphere. It involves a network of sensors, command-and-control systems, and ground-based interceptors launched from sites in Alaska and California.