Do you know that one missile, properly targeted, could degrade the electronic grid of the entire continental United States?

Do you also know that even North Korea has weapons capable of doing this?

Here's how it would work. Rather than target the warhead at land, enemies deliver their payloads from 25 to 300 miles above the Earth's surface. There, radiation from a nuclear explosion would interact with air molecules to produce high-energy electrons that speed across the earth's magnetic field as an instantaneous, invisible electromagnetic pulse. Such an explosion would release a pulse strong enough to disrupt power grids, electronic systems and communications over the lower 48.

The United States never has prepared for this threat because experts long assumed it wouldn't matter. An EMP attack, the theory goes, would come as a precursor to a full-scale nuclear exchange with our Cold War nemesis, the Soviet Union. At that point, the state of the power grid would be the least of our problems.

But today, we must consider a giant electromagnetic pulse (EMP) a significant threat on its own. The congressional Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack, calls EMP "one of a small number of threats that has the potential to hold our society seriously at risk and might result in defeat of our military forces." A scientist who has studied the issue says an effective EMP attack could set back countries dependent on 21st century technology by 100 years or more.

The commission's report stressed that the United States needs to figure out who, among both states and non-state actors, is capable of launching such an attack. Also, we need to know where we are most vulnerable, how we'd recover from such an attack and what it would take to protect our military and civilian systems.

Our military needs to retrofit some equipment to resist such attacks and insist that more new purchases come EMP attack-proof. Of course, the best defense against an EMP attack would be an effective missile-defense system that intercepts the missile before it reaches the United States.

It won't be easy, and it will be costly. Protecting electronics infrastructure requires that entire systems be encased in a metallic shield. Antennas and power connections must be equipped with surge protectors, windows must be coated with wire mesh or conductive coating and doors must be sealed with conductive gaskets.

Fiber optic cable is not vulnerable to EMP, so it's in our interest to replace as much copper cable with fiber optic as possible. We also need to protect the switches and controls that guide microelectronics in conjunction with fiber-optic cable.

In the future, such protections can be engineered into these products and structures, at an added cost of 1 percent to 5 percent of the price.

One step the United States can take for free is to develop a policy -- and publicize it -- that it would respond with devastating effect against anyone that launches an EMP strike. We also should ensure that portions of our military are protected against EMP, field active defenses (such as a missile shield) and passive defenses (such as switching to fiber optic where possible) to reduce the damage done by such an attack and increase the risk for a would-be aggressor. Hopefully, these changes, taken together, would deter anyone from launching such an attack.

We should make it a priority to develop a plan not only to respond to such an attack but to recover as quickly as possible -- and do so soon. All over the world, countries are attempting to join the nuclear club. Most would not be considered America's allies. Failure to address this significant vulnerability only encourages leaders already hostile to us to attempt to exploit this weakness.

There is real danger here. The technology that makes us the leader among the world's nations only makes us more vulnerable. We're unprepared now. That needs to change.

--Jack Spencer is a senior policy analyst for defense and national security in the Davis Institute for International Studies at The Heritage Foundation (heritage.org).