Over the last fifty years American defense electronics firms, especially Lockheed and Raytheon have developed a series of phased array radar system technologies that first appeared as the SPY-1 Aegis system, which was designed for use on warships. What made the Aegis system so successful was its ability to rapidly incorporate new hardware and software that greatly increased capabilities without the need to install a new radar system. There have been dozens of major modifications and upgrades and, to make those easier to keep track of major models of this new technology the navy used their initial designation SPY-1 (Array, Navy/Search Protect, Yellow 1) to note major types and sizes of the radar system by just changing the number. As a result, the latest version, SPY-7, has longer range and a more powerful LRDR (Long Range Discrimination Radar) capability that enables it to more precisely identify, or at least describe small objects hundreds of kilometers distant. This makes it possible to detect smaller ballistic missile warheads and determine which of them are decoys. Add to this the NCR (Network Cooperative Radar) capability and many ocean and land based radars equipped with this feature can create a larger view of what is out there and enable potential threats to be detected earlier and tracked longer. This is critical for defending against hypersonic missiles.

The SPY system also allows for the rapid introduction of newer, lighter and more powerful hardware. New microprocessor technology, like upgrading older gallium arsenide chips to more efficient nitride gallium technology. This upgrade made possible lighter and more powerful components and capabilities without exceeding a ship’s ability to provide the needed electrical power.

Another useful capability is easily creating more compact versions of Aegis systems. In 2009 Raytheon introduced SPY-5, or "Aegis Lite" for use in smaller (under 1,000 tons displacement) ships. SPY-2 is the anti-missile version of Aegis. SPY-3 and 4 were designed for new warships and combined the features of five different types of radars. SPY-5 takes care of air and surface search, plus fire control, and anything else you need radar for. The smaller (than SPY 1-3) uses only three flat phased array surfaces to cover all around the ship. The SPY-5 was also designed to be compatible with existing power supplies and electronic systems in Western ships. With SPY-5, Raytheon seeks to bring "Aegis technology" to many more users. About the same time SPY-5 appeared, SPY-6 was being put together to provide a more capable Aegis system for existing destroyers and frigates.

There are currently over a hundred Aegis equipped warships and the new versions are meant to expand that to several hundred, including land-based Aegis. Back in 1973, when Aegis was a new and expensive, but potentially revolutionary, system using 3-D radar. It used phased array technology, where the radar consisted of thousands of tiny radar transmitters that could be electronically aimed in different directions. Initially Aegis could track over a hundred targets, nearly 200 kilometers from the ship. Aegis was more than just a radar system, it was a tightly integrated combat system that gave the captain unprecedented "situational awareness" of what was around the ship in the air, on the surface, and under water. The Aegis radar not only tracked targets, but controlled Standard anti-aircraft missiles for long range shots, until a missile’s onboard radar could pick up the target and destroy it. Phased array radar was more difficult to jam and, in general, was way ahead of what any other navy has, and it still is. The latest version of Aegis and Standard missiles can shoot down ballistic missiles and low orbit space satellites. The AESA radar can also be used as an offensive EW (Electronic Warfare) weapon,

Development on Aegis began in the 1960s and in 1973 the first seagoing Aegis radar, mainly for testing purposes, went to work. Ten years later, the first Aegis equipped warship, the cruiser USS Ticonderoga, entered service and was decommissioned 31 years later with an Aegis system that had been upgraded several times. Aegis has turned into a concept that can easily be modified, upgraded and add major improvements quickly. Its usefulness can be measured by the growing number of export customers and efforts by other major powers to copy it.