On May 13, 1935, a small convoy-two Royal Air Force lorries, a couple of cars, six men-pulled into the seafarers’ village of Orford, about 150 kilometers northeast of London. Armed with some crude equipment, the men quickly set up shop in abandoned air force huts. Their secret mission: to save the United Kingdom from air attack. It was almost five years to the day before Hitler’s invasion of Western Europe. But their early start developing the technology now known as radar proved critical in warning of approaching bombers in the Battle of Britain-saving thousands of lives and ultimately forcing the Nazis to abort plans to invade Great Britain.

Whenever the debate about U.S. development of a missile defense system heats up-and this month marks the 20th anniversary of the “Star Wars” speech in which Ronald Reagan proposed a system to render nuclear weapons “impotent and obsolete”-I think of Britain’s radar pioneers. The analogy is far from perfect. Success for the British meant shooting down a small percentage of enemy bombers; in defending against a nuclear attack, even a 95 percent kill rate could mean atrocious losses. Still, there are striking parallels. Like today’s nuclear missile threat, the threat to England in 1935 was vague. Radar then was completely unproved, as is missile defense these days (”Why Missile Defense Won’t Work,” TR April 2002). And like many of today’s experts, leading authorities believed an effective defense was not feasible. As former prime minister Stanley Baldwin had famously told the House of Commons, “the bomber will always get through.”

So let me be blunt: given the stakes, there can be no excuse for not immediately pushing development of a missile defense system. This is not to say, however, that I wholeheartedly back the Bush administration’s program, which might deploy the first elements in Alaska as early as next year. In fact, I don’t support this plan, because it appears that certain important issues are not getting proper attention. In particular, two questions must be addressed: How narrow is our definition of missile defense? And, Is the system being deployed on the right scale and within a smart strategic framework?

Let’s start with the definition of the problem. The Clinton administration sought to intercept intercontinental ballistic missiles (ICBMs) only in midcourse-after reaching space but before reentry. Many experts, though, back boost phase defense, in which interceptors are deployed from bases or ships near enemy positions to destroy missiles before they reach space. This approach is both cheaper and technically easier, although it raises different geopolitical and logistics issues. The Bush administration, to its credit, has broadened the definition of missile defense and is now pursuing both boost phase and midcourse interception. In fact, its plan is to have as many as four shots instead of one at each enemy missile-a big reason the budget skyrocketed from $5.3 billion to $7.8 billion in fiscal 2002.

So far, so good. But in addition to ICBMs, cruise missiles also pose a potentially huge threat. ICBMs fly high and fast. Cruise missiles fly low and (relatively) slow. Stopping them presents distinct signal-processing challenges and will require radars that look in different directions and likely on different frequencies-and even different or substantially modified antimissile weapons. Yet while we are pouring billions into ICBM defense, the United States is vastly underinvested in cruise missile defense. In fact, says Owen Cote Jr., an associate director of MIT’s Security Studies Program, when it comes to cruise missiles, our plans include “no significant defense at all.”

Now let’s look at deployment. The Alaska-bound system, which targets midcourse interceptions, hasn’t come close to proving it can discriminate between real missiles and the decoys that any real attack would almost certainly employ. The main advantage of such a system is that it can defend against missiles launched from almost anywhere, whereas boost phase systems must be deployed in the vicinity of specific threats. But since we aren’t facing attacks from almost anywhere, a more reasonable first step would be to deploy boost phase systems around such troubled areas as North Korea and to follow with midcourse systems as we advance the technology. Or, as Cote puts it, “Get in soon on a reasonable scale in a way that’s tailored to countering real threats, not imagined ones.”

Of course, even a perfect missile-defense system can never make nuclear weapons “obsolete” or guarantee the United States won’t be attacked-be it by conventional aircraft or a terrorist operation. But missile defense needs to be pursued. Intelligently. The answer isn’t to rush ahead with unproved systems. It’s to roll out a defense in phases, at first deploying a limited system comprising technologies that are known to work and adding layers as new elements prove their effectiveness. At the same time, we cannot neglect development of a nationwide system to counter cruise missiles, so that sometime in the next 10 to 20 years we have an integrated, well-tested, comprehensive defense against both types of attack.

Only then will we have a reasonable chance of ensuring that the missile won’t get through.