Introduced in 1983 as the heart of the Aegis Combat System and the new Ticonderoga class Guided Missile cruiser, the AN/SPY-1 multi-function, phased array radar was a radical departure from prior conventional radar systems. The AN/SPY-1 held several advantages over earlier radars; First, where a conventional radar such as the AN/SPS-49 must sweep through a 360 degree arc looking for targets, and can only see those targets while they are within the radar's rotating ""cone"" the AN/SPY-1 radar is made up of four flat panels on the ship's superstructure which continuously radiate in all directions simultaneously, thereby allowing the system to acquire multiple targets coming in from multiple directions. Second, while a second radar is required to direct weapons to the target once it is acquired by the search radar, the phased array SPY-1 is capable performing both tasks simultaneously.
Radiating four million watts of power, the AN/SPY-1 can acquire and track targets as far out as 250 miles and as far up as low Earth orbit. In addition, the phased array system can track 100 targets simultaneously and engage them automatically, prioritizing targets by threat characteristics. There are currently four versions of the SPY-1 radar in service. Block I, the SPY-1A, was introduced with the USS Ticonderoga (CG47) and installed through the USS Philippine Sea(CG 58). Block II, the SPY-1B and it's later upgrade, the SPY-1B(V), was installed on the USS Princeton (CG59) and all subsequent Aegis cruisers, through USS Port Royal (CG 73). Introduced on July 4, 1991, the Arleigh Burke class Guided Missile destroyers are all equipped with the improved AN/SPY-1D. Finally, there is a reduced capacity version of the SPY-1D, designated the SPY-1F, available for installation on frigate sized vessels. While the United States does not currently intend to back-fit any of its Oliver Hazard Perry class frigates with the SPY-1F, the system is available for export.