Israel's Iron Dome missile shield
1. Enemy fires missile or artillery shell
2. Projectile tracked by radar. Data relayed to battle management and control unit
3. Data analysed and target co-ordinates sent to the missile firing unit
4. Missile is fired at enemy projectile
The Iron Dome has its roots in the 2006 conflict Israel fought with Hezbollah, the Islamist group based in southern Lebanon.
Hezbollah launched thousands of rockets, causing huge damage and killing dozens of Israelis.
A year later, Defence Minister Amir Peretz announced the state-run defence firm Rafael Advanced Defense Systems would develop a new missile defence shield.
The system took years to develop and came on line in early 2011.
It was tested in combat for the first time in April 2011, when it knocked out a missile fired at the southern city of Beersheba.
During the current Gaza crisis, the system has been repeatedly praised by the Israeli military.
By Saturday evening the shield had intercepted 245 rockets from Gaza in three days, according to the army.
Roughly 90% of the attempted interceptions were successful, the army said.
The latest Iron Dome battery to be deployed is in Tel Aviv, the commercial capital, which was previously thought to be out of range of rockets from Gaza.
But Gazan militants appear to have upgraded their arsenal, and the city has been repeatedly targeted in the first days of the latest bout of conflict.
Reuters news agency reported that the Tel Aviv battery was called into operation shortly after it was installed, knocking a rocket out of the sky as it was on its final approach.
The news agency said the Iron Dome's range appeared to have been tested to the limit by the Tel Aviv attack.
The Iron Dome is part of a huge range of missile defence systems operating over Israel, costing billions of dollars.
The Americans set aside more than $200m (£125m) to help Israel pay for the system, but concerns over its cost have persisted.
The system uses radar to track incoming rockets, and then fires two interceptor missiles to knock them out.
Each Iron Dome battery costs about $50m to install. So far, there are five batteries in operation, but officials plan to have eight more by next year.
Each Tamir interceptor missile costs roughly $60,000.
The shield's makers say it is cost-effective because the radar technology differentiates between missiles likely to hit built-up areas and those missing their target. Only those heading towards cities are targeted and shot down.
This still means that as of Saturday night Israel had spent roughly $29m on interceptor missiles in three days.