 Under these circumstances, the ships themselves must utilize multilayered defenses which have been built into them.For example, some warships, such as the U.S. Navy's guided missile cruisers, the guided missile destroyers, and the Royal Navy's Type 45 guided missile destroyer, use a combination of powerful and agile radar systems, integrated computer fire-control systems, and agile surface-to-air missiles (SAM) to simultaneously track, engage, and destroy several incoming anti-ship missiles or hostile warplanes at a time.The primary American defensive system, called the Aegis Combat System, is also used by the navies of Japan, Spain, Norway, and South Korea, and in three new guided missile destroyers of the Royal Australian Navy.