The incoming ICBM was flying at a speed of around 13,000 miles per hour. The Ground-Based Interceptor, or GBI, that hit it, was traveling even faster, at 15,000 miles per hour.

That is not the equivalent of hitting a speeding bullet with another bullet, as has often been said; it is arguably almost seven times more difficult, as the combined speed of a bullet and another one fired at it would be around 4,000 miles per hour.

The test was the first successful test of the much-criticized, long-delayed and problem-plagued ground-based interceptor program in four years. As we have noted in previous columns, five of the last 10 tests of the system were failures. In two of the last three tests before Friday, the interceptor's engines never ignited and the interceptors did not take off.

The basic reason for the previous failures of the program, and the underlying reason why Friday's test was so successful, was that Defense Secretary Donald Rumsfeld and his top civilian officials at the Pentagon through the first Bush administration were simultaneously fervent supporters of ballistic missile defense but ignorant of the immense technical engineering difficulties of getting it to actually work.

The basic problem was not one of design, but of the initial lack of careful and meticulous testing. Just building a relatively small rocket to fly at speeds of 13,000 to 18,000 miles per hour is a major undertaking in itself.

But it is enormously complicated by the need to also include precision electronics sensitive and accurate enough to guide the missile to a successful interception while still being robust enough to work accurately after surviving the enormous G-forces experienced when the interceptor accelerates to those speeds.

However, Rumsfeld and his top deputies were in such a rush to get the first missiles of the system deployed at Vandenberg and Fort Greeley, Alaska that that, as the Government Accountability Office later confirmed, they set aside several of the cautious, detailed Pentagon protocols for carefully component-testing the different parts of ballistic missiles to ensure their reliability before they were deployed.

However, Lt. Gen. Henry "Trey" Obering, head of the U.S. Missile Defense Agency, recognized the nature of the problem affecting the program and over the past two years his engineers and technicians, and those from the prime contracting companies, have been working around the clock to upgrade the reliability of the interceptors. Friday's success was the result of their efforts.

Even if it eventually works perfectly, the GBI program could not defend the United States against the multiple-reentry targeted vehicles, or MIRVs of the Russian Strategic Rocket Forces, the most destructive military force on the planet. They were never designed to. The SRF could flood the skies with far more missiles and warheads in any theoretical full-scale attack than 11, or 50, or even 100 GBIs could possibly stop.

Currently the SRF has an estimated 2,400 warheads -- enough to aim 10 of them at each of the 240 main population centers in the United States. That would include Austin, Texas, Bismarck, N.D. and Des Moines, Iowa as well as New York City, Chicago and Los Angeles. Also, Russia has been pushing ahead energetically with its efforts to make its ICBMs and their warheads more maneuverable and able to avoid GBI type interceptors.

The GBI system is primarily designed to protect the United States from nuclear-armed ICBMs that could be launched by so-called "rogue" nations like Iran or North Korea. Against that potential threat it is meant to be a credible deterrent.

The problems and failed tests plaguing the program were devastating to its credibility. And even Rumsfeld, usually the most optimistic of senior U.S. officials, went out of his way to play down expectations for Friday's test when he visited Fort Greeley a few days before.

However, the success of the test automatically gives the GBIs already deployed far more credibility. And it will also give a timely boost to the GBI program's champions in Congress. U.S. allies who have committed themselves to supporting and developing missile defense, especially Japan, may accelerate their orders for systems and speed up their deployment plans. A new chapter in the history of the BMD program has begun.

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