The AN/SPY-1 is a ship-based, passive phased array radar developed by Lockheed Martin for the US Navy. Using four complementary antennas in order to provide full 360 degree coverage, the AN/SPY-1 is an important component of the Aegis Combat System, which is computer controlled. This 3-dimensional, S-band radar has a range of 100+ nautical miles, and an azimuth of 360º. Up until the introduction of the AN/SPY-1, an ordinary mechanically rotating radar could detect a target when a radar beam struck that target once during each 360º rotation of the antenna; a separate tracking was then used to engage each approaching target. Now, the computer-controlled AN/SPY-1 is capable of bringing these functions into one system. The four fixed arrays of "SPY" send out beams of electromagnetic energy in all directions simultaneously, continuously providing a search and tracking capability for hundreds of target at the same time.
Although the AN/SPY-1 was fist installed on the the USS Norton Sound 1973, it became fully operational in 1983 on USS Ticonderoga as the SPY-1A. The SPY-1D was first installed on Arleigh Burke in 1991. The SPY-1F is a smaller version of the 1D designed to fit frigates. It is not used by the US Navy but has been exported to Norway.