By tracing the trajectory of the Palestinian missile within the first few seconds of its flight, the system could calculate whether or not it was heading for a populated area and therefore whether the firing of a defensive interceptor missile was necessary.

BBC: How did Iron Dome perform over course of Gaza clash?

Japan has deployed defensive anti-missile batteries at three locations in Tokyo, to protect the capital's 30 million residents.

BBC: UN chief Ban: Korea crisis could become 'uncontrollable'

The Phalanx is also being sold to Australia as part of the deal, extending the anti-missile defensive capabilities of one of America's most important Pacific allies.

CENTERFORSECURITYPOLICY: China's assymetrical strategy

Cancellation of the Zumwalt DDG-1000 program was the right move with more focus on building Arleigh Burke DDG-51 missile destroyers and improving their defensive capability.

CENTERFORSECURITYPOLICY: China's one world?

But Turkey allowed the missile batteries to be placed there only for defensive purposes, and NATO nations would have to agree before they could be used for offensive strikes against Syria.

CNN: Sarin in Syria: What's the United States' next move?

The advent of new technologies like hit-to-kill missile seekers and advanced signal processors greatly increased the defensive potential of the system while reducing the danger of collateral damage.

FORBES: Missile Defense Becomes A Navy Mission

Russia's hold on us is the Anti-Ballistic Missile (ABM) treaty, which essentially prohibits building defensive weapons.

CENTERFORSECURITYPOLICY: Beware a Clinton Arms Deal

Washington and Tokyo are working on a joint missile-defense shield, and South Korea is considering the purchase of American SM-2 defensive missiles for its destroyers.

NPR: Bush Calls for Unity, Condemns North Korean Tests