BOB ZUBRIN: What Do We Need? Missile Defense. When do we need it? Now.

The U.S. military has a fairly robust antimissile defense arsenal, including Patriot missiles, Aegis warships, Iron Dome technology, and Terminal High Altitude Area Defense (THAAD) systems. But these systems are designed to deal with short- to intermediate-range ballistic missiles. They are not capable of countering ICBMs, which come in much faster. So the missile defenses the United States now possesses are suitable for regional defenses, which is why we can share our defensive capabilities with South Korea, Japan, and Israel—allies who have adversaries or face potential threats from short- or intermediate-range missiles—but lack national coverage here at home.

Indeed, the American homeland is nearly defenseless against ICBMs. The one deployed system theoretically capable of countering ICBMs is the Ground-Based Midcourse Defense (GMD), which uses Raytheon SM-3 rockets to take out targeted warheads by direct impact. The GMD system, though, is much too small. There are currently only 44 GMD interceptors, with 40 located at Fort Greeley in Alaska and the remaining 4 at Vandenberg Air Force Base in California. There have been just 18 intercept tests of this system, of which only 10 achieved the goal of hitting their targets in flight, for a batting average of 0.556. Stats like that would be great for baseball, but not for national defense; they’d mean that if you’re facing incoming ballistic missiles and want a better than 90 percent chance of shooting them down, you’d need four anti-missiles in your battery for every incoming missile.

While Alaska is ideally situated for intercepting West Coast-bound North Korean missiles, the North Koreans could, with only modest improvements to their technology, bypass the Alaska-based system by firing directly over the North Pole, striking targets anywhere in the continental United States.

There are plans on the drawing boards for improvements to the GMD system—starting with the deployment of a “redesigned kill vehicle”—but those plans are years from becoming reality. And in the meantime, the number of GMD interceptors is expected to fall below the current number of 44 as today’s stockpile is used in planned tests or undergoes anticipatable retirement. Why, in the light of the present threat, is more not being done?

Why indeed? Though more should have been done 5-10 years ago.