In 2011, the U.S. Army asked American defense firms to develop a longer range weapon to use for base defense against rockets and mortar shells. Since 2006, the U.S. has been using a modified naval weapons (Phalanx) called C-RAM for this. This weapon has a range of about 2,000 meters and can knock down 70-80 percent of the rockets and mortar shells fired within range of its cannon. Phalanx and C-RAM were developed by Raytheon.
C-RAM uses high explosive 20mm shells that detonate near the target, spraying it with fragments. By the time these fragments reach the ground they are generally too small to injure anyone. At least that's been the experience in Iraq and Afghanistan. The original Phalanx used 20mm depleted uranium shells, to slice through incoming missiles. Phalanx fires shells at the rate of 75 per second. Another advantage of C-RAM is that it makes a distinctive noise when firing, warning those nearby that a mortar or rocket attack is underway, giving people an opportunity to duck inside if they are out and about.
Raytheon, the manufacturer of the AIM-9X air-to-air missile, proposed a system based on Avenger. This is a hummer equipped with a turret in back containing two missile pods (each containing four Stinger anti-aircraft missiles). Under one pod there is an M3P .50 (12.7mm) caliber machine gun. The weapons operator has use of a FLIR (night vision device) and a laser range finder. The new Raytheon AI3 (Accelerated Improved Intercept Initiative) weapon uses 87 kg Sidewinder missiles instead of the 10 kg Stinger, drops the machine-gun and uses the C-Ram fire control system and an upgraded radar. Raytheon had been working on firing Sidewinders from the ground (at aircraft or rockets) since 2009. The C-RAM has been used successfully in combat so it was not a surprise that the new AI3 system worked after a year or so of tinkering. AI3 has a range of 10 kilometers and has knocked down rockets and mortar shells repeatedly.
As impressive as this sounds, AI3 is inferior to the Israeli developed Iron Dome system, which has been in service since 2009 and has proven itself in combat. Israel has bought seven batteries of Iron Dome. Each battery has radar, control equipment, and 3-4 missile launchers (each with 20 missiles) and costs about $37-50 million.
Iron Dome uses two radars to quickly calculate the trajectory of the incoming rocket and do nothing if the rocket trajectory indicates it is going to land in an uninhabited area. But if the computers predict a rocket coming down in an inhabited area, a $50,000 Tamir guided missile is fired to intercept the rocket. This makes the system cost-effective. So far Iron Dome has shot down 85 percent of the rockets it calculated were headed for populated areas. The Tamir missiles used by Iron Dome weigh 90 kg and have a range of 70 kilometers against rockets, mortar shells, and artillery shells up to 155mm. Iron Dome can also shoot down aircraft and helicopters (up to 10 kilometers/32,000 feet).
The U.S. supplied much of the money and some of the technology needed to develop Iron Dome and could obtain Iron Dome systems for about as much as the Israeli Air Force pays. The Tamir missile costs half what the Sidewinder does and the Iron Dome has software that only fires a missile that is going to hit something you want to defend. The problem is moot now that the Department of Defense has cancelled plans to actually produce the AI3 weapon because of reduced need and budget cuts.