"...a single integrated grid of sensors from under the sea to space to bolster its air and missile defenses, U.S. Northern Command’s top general told the Senate Armed Services Committee Thursday.
“The first and most critical part [of this defense] is detection” to protect the lower 48 states and Alaska and Hawaii..."
Reference: U.S. Naval Institute
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"...Lockheed Martin, as the MDA’s prime contractor for Targets and Countermeasures, will deliver targets from Courtland to ranges around the globe to test Terminal High Altitude Area Defense, Aegis, Ground-based Midcourse, Airborne Laser, sensors and other Ballistic Missile Defense System elements – demonstrating both element- and system-level capabilities against current and future threats to the U.S., friends, allies and troops abroad. ..."
Reference: www.lockheedmartin.com .