There's a classic military technique for determining where to strike an enemy. You want your target to be something the enemy needs, something the enemy loves, and something that's not easily replaced.

We've been planning aerial bombing raids using this formula for decades now. So it shouldn't surprise us that our enemies do the same. They like to strike us in a manner that is sure to make us mourn, make us bleed, and weaken us.

Thinking about the methods that our enemies might use against us and the targets they might choose is an exercise that we don't undertake often enough. This kind of "red cell" exercise has two purposes: It keeps the threat present and real in our minds and it helps us determine what targets we need to harden.

The following is a quick look at where and how some of the leading experts on terrorism believe our enemies may strike. It's in no particular order because each scenario is a nightmare, and how do you rate a nightmare?

Snipers

No crime wave in the last decade instilled more fear than the Beltway Sniper attacks. For three weeks in October 2002, the entire Washington, D.C., metropolitan area was terrorized by random sniper attacks. People were shot as they walked into restaurants, as they walked out of stores, and as they pumped fuel into their cars. As the death toll mounted, climbing to 10 victims, people stopped leaving their houses, people literally ran into stores, and people crouched behind their cars as they filled their gas tanks.

All of this havoc was created by two men who had turned the trunk of a 1990 Chevy Caprice into a mobile sniper hide. This tactic has since been copied by Islamist snipers in Iraq to terrible effect on our troops. It's not much of a reach to think that some of these terrorist snipers can't wait to use their marksmanship skills here on the soil of the Great Satan.

Active Shooters

The terrorists have as much access to the news as the rest of us. They know about Virginia Tech and they surely know about Fort Hood. So whether it's lone wolves or groups of armed men, we can bet that the terrorists plan to hit us with active shooters.

Of course the nightmare scenario here is a Mumbai-style attack with multiple shooters going mobile through an urban area. For the Mumbai attack, the shooters arrived by boat. The principle reason for using water for the insertion was so they could bring their weapons into India. So don't think that just because your city isn't on water that it's necessarily immune to a Mumbai-style assault.

Responding to a Mumbai-style "swarm" attack will tax the resources of even the largest department. Imagine all of the calls to 911 from a panicked populace. Imagine all of the traffic jams and the chaos. It will be a mess. And every urban department needs to have a plan to deal with such an attack.[PAGEBREAK]

Car Bombs

Our enemies are as much creatures of habit as we are. They've been using car bombs for decades. And the reason is simple: These things are devastating. A favorite of both domestic and foreign terrorists, a car bomb packs a big punch.

There are two things that experts say local officers should always remember about car bombs.

The first thing you need to remember is that a simple parking violation could be a car bomb. So be careful and check out suspicious vehicles. Some terrorists-such as the Times Square would-be bomber-are really sloppy. If you see a smoking car, it may be a problem or just a poorly maintained car. If you think you have a bomb on your hands, call in the bomb techs.

The second thing you need to remember is that the first explosion may not be the primary attack. Terrorists can be very cunning. They know that a bomb attack is going to draw a lot of attention. And to their point of view, all those responders, all those firefighters, cops, and EMTs, are a juicy target. So beware of a second bomb targeting you. This is one of their favorite strategies in Israel.

Suicide Bombers

No tool in the terrorist's arsenal has been more effective than the suicide belt, vest, bra, etc. This tactic has been used by the Tamil Tigers, and it is a favorite of the Palestinians, al-Qaeda, and the Taliban.

We have yet to see the use of suicide bombers on American soil (unless you count 9/11 during which the hijackers essentially turned airliners into suicide bombs) but many experts believe this day is coming. Actually, they are puzzled as to why the enemy hasn't employed this tactic here.

Maybe the answer is that the terrorists don't currently have all of the elements in place to launch this kind of attack. To launch a suicide bomb campaign, they need a population of people willing to martyr themselves for the cause, some bomb makers, and some explosives. Of these three elements, the one they currently lack is the martyrs.

But they have two future sources for this raw material: They can import martyrs into the country like they did on 9/11 or they can radicalize people here. The Internet and other tools are making it very easy for the bad guys to radicalize disaffected Americans. So this source of martyrs may soon produce suicide bombers.

Officers need to be on the lookout for people who are dressed inappropriately, for example wearing heavy coats on a warm day. Suicide bombers are likely to target restaurants, entertainment venues, shopping centers, and other places where body counts will be high. Note: a favorite terrorist tactic is to combine active shooters with suicide bombers. So when answering an active shooter call keep in the back of your mind that there may be multiple gunmen and bombs. Note Two: Police and police stations are a favorite target of suicide bombers overseas.[PAGEBREAK]

Transportation

Nine years ago the bad guys used airliners as weapons of mass destruction. It's unlikely such a plot would ever work again since the passengers would likely realize that they had no chance of survival and fight back like the heroes of Flight 93. God bless them.

So the most likely type of transportation attack will be a bombing. Airplanes are juicy targets and bombs/bombers can be planted on them in a variety of ways.

But a bigger concern is actually commuter trains. The London and Madrid bombings prove how terrible a subway or commuter train bombing can be. Commuter trains are soft targets because security is difficult to effect, expensive, and disruptive. Can you imagine having TSA scan everybody before they get on a subway? It's just not practical.

So the likelihood of an attack on a commuter train is high because it achieves two major terrorist goals: a high body count and economic disruption. And it's an easy target.

Schools

This is something people don't talk about in polite company. It's horrible. It keeps many a terrorism expert awake at night. And here it is: Our enemy likes to kill and torture children.

And there's no better place to kill children than in a school. There are two ways that terrorists are likely to attack children. One is a Beslan-type attack in which a large group of terrorists take over a school and stall police response with false negotiations while they fortify the place. When they are ready they will kill everybody in the place and before they kill them they will torture them.

The only response that can possibly make a difference on something like this is a quick and aggressive response. Even one officer might be able to pin down the bad guys a bit and buy time for a more effective assault by more officers. If the bad guys get hours and days to harden the place, it's going to be hell to get it back and it's going to be hell for the hostages.

The second type of school attack is a lot easier for the bad guys to execute. All they have to do is come into a school and shoot the kids. It won't take an entire group of terrorists to execute such an attack. It could be one guy with a pistol. It could be a homegrown terrorist.

School attacks are highly likely because they achieve every goal of a terror organization like al-Qaeda. They terrorize, they hit people emotionally, and they have the potential to devastate the economy.

Infrastructure and Industry

Some of the foiled plots that al-Qaeda and their ilk have attempted before and after 9/11 have targeted airports, bridges, and other valuable infrastructure. Future attacks might include dams, hospitals, train stations, power plants, and hundreds of other valuable and hard to replace infrastructure elements. These places need to be watched and they need to be hardened.

Another choice target for a terrorist attack would be a chemical plant. To understand the potential devastation that could be wrought by such an attack, take a look at the Bhopal, India, disaster. The Bhopal chemical plant leaked toxic gas in 1984 and thousands died.

Any terror group anywhere in the world can call up Google Earth on the Internet and see detailed satellite photos of chemical plants and oil refineries in your jurisdiction. So you can bet that these facilities are on their target lists. Local officers need to work with these companies to make sure that these plants are as secure as possible.

Not If But When

There are, of course, other types of attacks that could happen. Terrorists could gain access to gas, or biological, or radiological material, or even nuclear weapons. And there is no doubt that they would be willing to employ such terrible weapons. But the logistics of staging such attacks make them complex and difficult to carry out. Which is why many experts consider them unlikely.

But no one can see the future. So we don't know exactly what the enemy will do or how he will do it. The one thing we do know is now that the Iraq War is winding down, Arab terrorists may once again turn their attention to hitting us where we live. Which means: The next terror attack on American soil is not a matter of if but when. And all American law enforcement officers need to be both vigilant to prevent such attacks and ready to respond to them when they happen.

Have you trained to respond to attacks on these targets? Do you think enough is being done to harden these targets? Tell us in the comments below.