Israel's 'Iron Dome' defense: Here's how it works

• Currently, 5 Iron Dome batteries are deployed in Israel
• Missiles cost about $40,000 a piece
• Rockets headed toward open areas are allowed to land

JERUSALEM (AP) — In four days of fighting against Gaza-based militants, Israel has used a missile-defense system called "Iron Dome" to intercept rockets fired at populated civilian areas. It says the new home-grown system has been a tremendous success. As of Saturday evening, the military said it had shot down some 240 incoming rockets, more than half the number of projectiles launched into Israel since Wednesday.

Here's a quick look at the system:

• Produced by Israeli-based Rafael Advanced Defense Systems, Iron Dome is meant to shoot down rockets and artillery shells with ranges of up to 45 miles. It has been operational since 2011.

• How it works: The system detects launches of rockets and quickly determines their flight path. If it is headed toward populated areas or sensitive targets, it fires an interceptor with a special warhead that strikes the incoming rocket within seconds. Rockets headed toward open areas area allowed to land.

• Currently, five Iron Dome batteries are deployed in Israel. Most are located in the south near Gaza. A fifth battery was deployed outside Tel Aviv on Saturday, two months ahead of schedule. Hours later, it shot down a rocket headed toward Tel Aviv.

• Missiles cost around $40,000 a piece. In 2010, the U.S. provided $200 million to expand development. Additional funding is currently being considered, with $70 million already allocated for the 2012 fiscal year.

• The system is part of what Israel calls its "multilayer missile defense". It is meant to protect against the tens of thousands of short-range rockets possessed by militants in the Gaza Strip and Hezbollah guerrillas in Lebanon. Israel has also deployed its "Arrow" missile defense systems for long-range threats from Iran. The military says its new "David's Sling" system, being developed by Rafael to stop medium-range missiles, will be activated by 2014.