Interoperability is the ability of a system to work with or use the parts or equipment of another system; it is also the goal and end state for all theater security cooperation exercises that take place around the world every day. Just as each military and police unit requires interoperability of weapons, tactics, and communications, the need for this type of relationship at the multi-national level has never been more vital. Interoperability is achieved through theater security cooperation exercises, which most commonly involve infantry-type military tactics and training. However, due to the new looming international terrorist threat faced today, law enforcement–based exercises of this nature are beginning to gain speed.