ISRAEL has long been protected by its famed “iron walls”. Now those walls have a rooftop. Israel’s arms manufacturers have devised an anti-missile system, offering what they call an “Iron Dome” overhead. Iron Dome’s manufacturers claim it is the fastest and most reliable such system to date, able to shoot down missiles with a launch-to-impact time of 15 seconds. The $1-billion programme, subsidised by the United States, has served Israel well in Operation Protective Edge, its recent campaign against Hamas in Gaza. Palestinian militants have lobbed almost 1,000 missiles into Israel, but Iron Dome's interceptors have struck down 87% of their targets, according to the Israelis, allowing life in Israel’s cities to proceed more or less normally. How does it work? Iron Dome is the short-range component of Israel’s three-tier anti-missile defences. The other two elements are David’s Sling, still under development, which is intended to shoot down targets in the atmosphere, including over the Mediterranean; and the Arrow system, designed to intercept longer-range ballistic missiles in space. As soon as enemy rockets are launched, Iron Dome’s radar tracks their trajectory, calculates their impact point and launches a missile which within seconds locks onto the rocket and shoots it down. Each interception costs about $60,000, but its architects claim to have saved Israel billions in physical damage and economic impact, as well as loss of life.

The system has overcome many teething problems. Initially, Israel’s defence planners were wary of deploying it over airports, lest it respond to aircraft and target them too. Commanders have since developed a country-wide network identifying all friendly airborne traffic, ensuring the Iron Dome's missiles target only the unknown. Other problems remain: even when rockets are successfully shot down, potentially lethal shrapnel falls from the sky. “Whatever goes up, must come down,” says Uzi Rubin, a designer of the Arrow system. And the country’s highways and rural areas remain exposed. Farmers, often migrant workers from Thailand, cower among their crops. Israel’s 200,000 Bedouin, many of whom live in shanty towns, have nowhere to hide. Labourers expanding Israel’s infrastructure look to the sky and pray. On July 14th a rocket seriously injured a ten-year-old girl in her shack in the shanty town of Lakiya. Even over cities, one in ten incoming projectiles slips through.

Some wonder if Iron Dome's main problem is in fact a political one. The system's success means that Binyamin Netanyahu, the Israeli prime minister, has been able to use Iron Dome to maintain his policy of conflict management, with less fear of retaliation. “Iron Dome has altered the calculus of Israel’s political echelons in ways they have yet to understand,” says a former senior official. “It allows Israel to resist internal public and military pressure for a quick end to the conflict, and keep bombing Gaza.” It also provides some degree of immunity against other neighbours armed with missiles, such as the Lebanese Shias' Hizbullah militia, or Syria, perhaps making the agreement of a lasting peace settlement seem less urgent. Nonetheless, as air-raid sirens sound, most Israelis are glad to have the protection of the Iron Dome.

Dig deeper:

No matter what Israel’s prime minister says, the conflict with the Palestinians cannot simply be “managed” (July 2014)

Chart: Gaza in numbers (July 2014)

Neither Israeli nor Palestinian leaders seem willing to halt the destruction (July 2014)