Phalanx radar can spot incoming missiles out to about 5,000 meters, and the 20mm cannon is effective out to about 2,000 meters. . . . . since 2003, there have been two major Phalanx mods. In one, the Phalanx was adapted to use on land, against rocket attacks. Using a larger artillery spotting radar, Phalanx directs its fire at incoming mortar shells and rockets. Not all the incoming stuff is hit, but a lot of it is . . . The second mod is for shipboard use, and changes the software so the Phalanx can be used against small boats . . . . Israel is looking at the anti-rocket version[.]
The business end of the phalanx isn't fundamentally much more sophisticated than a heavy World War I era machine gun. It doesn't take out incoming ordinance with lasers, kinetic energy weapons, or anything fancy like that. It is just a big, high rate of fire slug thrower. Likewise, radar itself isn't revolutionary technology. Radar has been used for military purposes for half a century. The sophisticated piece of the system is its lightning fast interpretation of incoming radar signals coordinated with its ability to automatically aim the weapon at fast moving incoming targets. The real value is all in the software.
Despite this, Phalanx is arguably the make or break technology for the modern Navy. Anti-surface ship missiles have grown so potent that anything smaller than an aircraft carrier can be brutally damaged by a single hit, even if the ship is relatively thick hulled. Ships are vulnerable to large barrages of enemy missiles (launched from ships or aircraft), attacks from small boats, missiles and enemy submarines. Phalanx is the primary defense against two of these threats. If it doesn't work, the surface fleet is toast. For ground troops, meaningfully effective active anti-artillery defenses represent a new and important capability.
While a lot of money and talk goes into anti-ballistic missile defenses, far more prosiac weapons are a far more immediate threat to Americans and their allies.