Theater High Altitude Area Defense (Thaad) and sea-based upper-tier defenses are being viewed by the U.S. Department of Defense as promising technologies for their Ballistic Missile Defense (BMD) program. Patriot PAC-2 and PAC-3 and the sea-based lower tier defenses will act as back-up for targets missed by the upper tier and protect high-value targets such as airfields, ports, headquarters, and population centers. Airborne lasers will aim to destroy missiles during the boost phase, when their rocket motors are burning and before they can deploy warheads, decoys, or submunitions. These will be managed by a Theater battle management system which will coordinate the system's many components by providing command, control and communications.