In December, the Missile Defense Agency placed its eighth interceptor missile into an underground silo at Fort Greely, Alaska. Two more interceptors already have been emplaced at Vandenberg Air Force Base, Calif. These anti-ballistic missiles are designed to destroy attacking long-range enemy ballistic missiles.

"The interceptors are part of an integrated system of ground, sea and space-based sensors, ground and sea-based radars and an advanced command and control, battle management and communication system designed to detect and track a hostile ballistic missile, then launch and guide an interceptor to destroy the target warhead before it can reach its intended target in any of our 50 states," MDA spokesman Rick Lehner said.

The interceptors "can be brought to alert status in an emergency but they are not yet on 24/7 alert," Lehner added. "'Shakedown' training sessions are still ongoing by U.S. Strategic Command and U.S. Northern Command."

An airborne laser is also being developed and tested. The ABL weapons system is a chemical oxygen iodine laser fitted to a heavily modified Boeing 747. The laser will destroy a missile by heating its metal skin until it cracks, causing the boosting missile to fail, according to the missile agency's Web site.

The anti-ballistic missiles in Alaska and California use "hit-to-kill" technology: They destroy incoming enemy missiles by physically colliding with them. This task often has been described as hitting a bullet with a bullet.

"It's difficult hitting something that is traveling at 15,000 miles per hour, especially when trying to avoid decoys and other interference," Lehner said. "Many people think that we have always had the capability to shoot down a missile that was aimed at a city or town in the U.S., but it is only very recently that we have developed the technology."

The Missile Defense Agency has tested its hit-to-kill interceptor technology many times over the past several years. "A total of nine planned ground-based intercept tests have taken place since 1999; five have resulted in successful intercepts," Lehner said.

Eight sea-based tests since 2002 have resulted in seven successful intercepts, he added.

The road to building a missile defense shield has been long and arduous. The history of missile defense can generally be divided into two eras. The first spanned three decades from the end of World War II to 1976, when the United States briefly instituted the Safeguard missile defense system. Nuclear-tipped interceptor missiles defined this era, MDA chief historian Lawrence Kaplan said.

According to the agency's Web site, "the origins of the U.S. missile defense program may be traced to the Nazi missile program of World War II, which included plans for the world's first intercontinental ballistic missile. Learning of these German plans after the war, the U.S. Army Air Forces, predecessor of today's U.S. Air Force, began long range studies of interceptors that could destroy attacking ballistic missiles."

The Safeguard complex in North Dakota was an operational anti-ballistic missile system that defended American intercontinental ballistic missile silos. It did not defend American cities. The complex was deactivated in 1976 after being operational for less than four months. Congress shut it down due to technical limitations and the restrictions on missile defenses contained in the Anti-Ballistic Missile Treaty.

The ABM Treaty was a bilateral treaty that sprung out of the Strategic Arms Limitation Talks between the United States and the Soviet Union begun in the 1960s. The treaty was signed in 1972, and it limited certain types of technological advances and testing, among other things.

The second era of missile defense began on March 23, 1983, when President Reagan gave a landmark speech in which he proposed the Strategic Defense Initiative with the intent of making nuclear missiles "impotent and obsolete."

The media famously dubbed Reagan's initiative "Star Wars."

The SDI goal was to develop non-nuclear missile defenses to neutralize Soviet missiles. The U.S. was concerned that the Soviets had developed a first-strike capability, which would allow them to launch a knockout blow against U.S. interceptor missiles and then destroy the United States with a second volley of ICBMs.

On a personal level, Reagan hated the concept of mutually assured destruction, which was a cornerstone of U.S.-Soviet relations at the time. "It is better to save lives than avenge them," he said.

A paradigm shift has taken place since the end of the Cold War and the terrorist attacks of Sept. 11, 2001. With this shift in mind, President Bush withdrew the United States from the ABM Treaty, freeing the U.S. from its restraints.

"The circumstances affecting U.S. national security have changed fundamentally since the signing of the ABM Treaty in 1972," according to a White House fact sheet. "The attacks against the U.S. homeland on Sept. 11 vividly demonstrate that the threats we face today are far different from those of the Cold War."

In some government and scientific quarters, there are misgivings about the need for missile defense. Simply put, some people don't believe the technology is yet ripe and they don't see the threat; therefore, they can't justify the monetary allocation.

To missile defense advocates, however, the threat is all too real.

"Iran and North Korea are two countries that have been spending a great deal of time and money to develop several different types of advanced ballistic missiles, including a type that could possibly reach the U.S. homeland with a weapon of mass destruction in the near future," Lehner said.

Iran has successfully flight-tested its medium-range Shahab-3 missile, and is believed to be developing nuclear capabilities.

In August 1998, North Korea caused a stir when it fired its Taepo Dong-1 missile over Japan. This was especially troubling because "the North Koreans demonstrated important capabilities associated with ICBMs, including staging and the use of a third stage on the missile," according to MDA's Web site.

"There are more than 30 countries now with ballistic missiles," Lehner said, "with ranges varying from short to long-range. Many are hostile to the U.S., or our friends and allies."

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