The computer-based command-and-decision element is the core of the Aegis Combat System. This interface makes the ACS capable of simultaneous operation against almost all kinds of threats. The Aegis Ballistic Missile Defense System (BMD) program is intended to enable the Aegis system to act in a sea-based ballistic missile defense function, to counter short- and medium-range ballistic missiles of the variety typically employed by a number of potential opponent states. As of January, 2014, the US and Japan were the only countries to purchase or deploy the Aegis BMD.