tribal strife in the wake of the collapse of a totalitarian regime that has ruled the country with an iron fist for so long. Some neighboring governments will want to participate in this endeavor the better to influence the outcome of the internal struggle for power. Although Arab and Turkish peacekeepers will help legitimize the operation, this advantage must be weighed against the dangers of creating opportunities for meddling. The Iraqi people are likely to want to jealously guard their newfound independence and, like the Afghan people, will probably prefer American peacekeepers to those from neighboring countries.

Why does such a peacekeeping force have to be large, and why must it be led by Americans? After all, the International Security Assistance Force in Afghanistan has neither of these characteristics.

There are several reasons. First, ISAF is not going very well in Afghanistan, so this is a poor model for comparison. Indeed, the Bush administration admits as much at present, but still imprudently hopes that other countries will simply volunteer to beef up and expand the mission. Second, Iraq's Kurds in particular might well be tempted to try to secede absent a strong unifying national security force. Third, Iraq is in a region where cross-border aggression is more common than is the case for Afghanistan. Iraq's neighbors might well make trouble in a destabilized Iraq. Fourth, Iraq has a much larger army than did the Taliban, and the United States hopes to spare much of it in any future war, partly to avoid creation of the very type of security vacuum just noted. But we do not know who within that army is dependable and who may be bent on seeking vengeance against U.S. forces or internal foes. Weeding out bad actors, while also improving training and discipline, within the Iraqi military will take time and effort. Fifth, and relatedly, the overall importance of the Persian Gulf region may exceed that of Afghanistan (though that is open to some debate, to the extent that Afghanistan could again become a sanctuary for Islamic extremists). Helping create a stable, democratic Iraq could have immense benefits for U.S. interests in general, justifying a substantial effort.

How many forces would be needed to occupy Iraq? Various studies have been done, based on military history and the population, military capabilities, territorial size, and other characteristics of the country to be occupied. For example, work done by the Army's Center of Military History suggests that 100,000 occupying forces could be needed.2 Indeed, if anything that estimate seems low: NATO's stabilization mission in Bosnia, a country less than one-fifth the size of Iraq by population or territorial size (and also a country with three main ethnic groups), began with 50,000 forces and is still about 20,000-strong. Simply scaling those numbers for a bigger country, the standard practice when estimating policing and occupying needs, suggests that an initial force might have to number more than 200,000 and that a residual force seven years later might still total 100,000.

Assume for the sake of planning a force that is composed 100,000 to 250,000 occupying forces in its first year, and then 50,000 to 125,000 troops by its fifth year. Assume further that 15 percent to 25 percent of the total strength is American. Those estimates translate into possible U.S. requirements of roughly 15,000 to 60,000 troops the first year and anywhere from 7,500 to about 30,000 U.S. troops half a decade later.

The gradual drawdown would presumably continue thereafter, and the mission might last a decade or so once all was said and done.

How could such a large U.S. effort be sustained? For a military of 1.4 million, that may not appear difficult, but as the Armed Services Committee knows well, today's military is already working very hard to maintain more than 250,000 personnel abroad, including more than 100,000 at a time deployed away from permanent bases and families. Given rotation base issues, moreover, sustaining a deployment of say 20,000 troops tends to require about 100,000 in the force structure.

To be sure, some rather drastic measures could be adopted to ease the problem. For example, U.S. troops might leave Bosnia, and reduce their presence on Okinawa-two other places where forces deploy away from families-in order to facilitate a deployment in postwar Iraq. But it would be hard to free up more than 10,000 personnel in that way. This added demand would be onerous. It could require a combination of sustained reserve activation and even more difficult work for active-duty U.S. personnel, leading to poor quality of life and renewed problems with recruiting and retention (just after those problems have been largely solved by the work of the Congress and the last two administrations over the past half decade). It would not require a draft. But it could require other creative approaches, such as an alternative approach to joining the military involving shorter enlistments for those willing to put in 18 to 24 months of service (as suggested by Charles Moskos and others). In short, this mission could require some unusual and potentially rather expensive policy options. Annual costs could plausibly range from $5 billion to $20 billion.

I should not dwell only on the negatives. Occupying Iraq would be hard, but could have real benefits. Even the possibility of a U.S.-Iraq alliance, or a collective security structure involving the region's democratically inclined countries, could be given serious attention. This is not the place for an elaborate discussion, but suffice it to say that the process could remake the region's basic security dynamics as much as the aftermath of World War II and the Korean War reshaped Europe and East Asia. Such a possibility is a definite and major plus in favor of the argument for overthrowing Saddam-provided, of course, that the long-term work to stabilize and rebuild the country follows the military victory. Nation building would be needed, plain and simple.

II. ESTIMATING CASUALTIES IN A WAR TO OVERTHROW SADDAM

How many casualties might result if the United States and any coalition partners invade Iraq to overthrow Saddam Hussein's regime? How important is this issue for policymaking purposes over the coming weeks and months? Prior to Operation Desert Storm, several military experts estimaed that U.S. losses might wind up in the range of 5,000 to 10,000, and the Pentagon expected even higher numbers of killed. In contrast, actual American losses were just under 400 (of whom about 150 were killed by direct enemy action, the others being lost in accidents or friendly-fire episodes). Is it possible to make more accurate predictions this time around?

The following develops two central themes. First, the likely numbers of U.S. military personnel killed in a future war to overthrow Saddam could plausibly range from roughly

100 to 5,000, with total numbers of wounded about three to four times as great. This range is wide. But it is important to recognize that, based on available methodologies for predicting combat outcomes, anything in this range is plausible. Those in the public policy debate who insist that any war would be a walkover have the onus on them to explain why. At the same time, there would appear to be little chance of any war against Iraq bogging down into the type of quagmire in which combat could last years and entail many many thousands of American deaths. Invading Iraq would not be another Korea or Vietnam.

The second main theme is that Iraqi civilian casualties could be substantial in such a war, given the assumption that it would unfold largely in Iraq's cities. In approximate terms, casualties might be ten times as great as those of the U.S. military, if not more. This fact could pose pressures and problems for any Arab governments supporting the United States in such a war. Among its other implications, this is a strong argument for trying to defeat Iraq rapidly and with overwhelming force, so that the pressure of the "Arab street" can be contained. Civilian casualties due to clandestine or terrorist attacks are also possible in places such as Kuwait, Israel, and the United States, with plausible mortality ranges in the high hundreds of individuals.

The War Scenario

Consistent with military and strategic logic, and with leaked Pentagon war plans from the summer of 2002, I assume that a war to overthrow Saddam would involve about 250,000 American forces. The Afghanistan model of warfare, in which small numbers of U.S. special forces and American airpower work with indigenous opposition groups to fight government forces, would almost surely not work in Iraq, as discussed further below. That is due to relative weakness of the Iraqi opposition as well as the Iraqi military's ability to hole up in cities, where American airpower is far less effective than in open terrain. Modest-sized operations, involving perhaps 50,000 to 75,000 U.S. troops, are somewhat more promising. But they would run the risk of encountering serious difficulties in the urban centers of Iraq. Relatedly, Iraqi forces would be less likely to capitulate quickly if they sensed they had a chance to prevail, increasing the chances of a prolonged urban battle under such circumstances.

This is not to say that a larger operation would have to mirror Desert Storm in its basic concept. The invasion might involve rapid airborne or commando strikes against Iraqi command and control assets as well as weapons of mass destruction sites in the earliest hours of combat, even as main invasion forces march more slowly through Iraq towards Baghdad and other cities. It might also use relatively small teams of American ground forces-perhaps brigade-sized units of several thousand troops each-to try to lure Iraqi forces out of the cities into regions where they would be more vulnerable to American airpower (and to lure out defectors to join U.S. forces). These sorts of "insideout" tactics would try to avoid the delays inherent in a mechanized march from Kuwait and other neighboring countries to Baghdad. But they would be gambles, and the United States would need backup forces in place in case the gambles did not pay off.

Forecasting Casualties in Infantry and Urban Combat

Operation Desert Storm and, more recently, Operation Enduring Freedom in Afghanistan probably do not provide much insight into the likely nature of a future war in Iraq. Saddam seems unlikely to place many of its forces in the open in a future war. Because Iraq knows its weaknesses against the U.S. military in open settings, and because it is Saddam Hussein's regime and weapons of mass destruction capabilities that would be at issue in a future war, one has to assume that the combat would be primarily urban.

This fact immediately changes the calculus of a future war by comparison with Desert Storm. To begin, airpower would be much more difficult to employ against Iraqi forces that could intersperse themselves with civilian vehicles and populations. This type of tactic was employed near Basra during Desert Storm, and has been employed in the subsequent eleven years as Iraqis have sought to place valued military assets near civilian populations to make it harder for the United States to bomb them. Iraqi forces have much better cover within cities, or even forested regions, than in open desert. As one further demonstration of this rather obvious fact, recall that even after eight years of further modernization after Desert Storm, NATO airpower was of quite limited effectiveness against small groups of Serb forces operating within forests, towns, and civilian populations in the Kosovo war. If U.S.-led forces tried to fly low to find enemy forces against this complex backdrop, they would have to contend with an Iraqi air defense network consisting, among other things, of some 6,000 air defense guns and 1,500 surface-to-air missile launchers (including man-portable SAMs).3

Nothing about new technology and new warfighting concepts associated with the socalled revolution in military affairs seems likely to radically change the challenge of urban warfare anytime soon. For example, recent Marine Corps experiments incorporating such new concepts suggested that U.S. troops could still suffer quite high casualties in urban combat.

Historical Parallels

Two recent conflicts may provide better indicators of the likely nature of a future U.S.Iraq war: the 1989 invasion of Panama and the 1993 U.S. experience in Mogadishu, Somalia. In December, 1989, U.S. forces overthrew Panamanian strongman Manuel Noriega and defeated his armed forces. About 22,500 American personnel participated. The operation involved simultaneous nighttime airborne operations against 27 objectives throughout the country. Special forces infiltrated key sites shortly before the airborne assaults to take down Panamanian communications and oppose any attempts by Panama to reinforce its forces under attack. The massive, simultaneous assault against Panama 's 4,400-strong defense forces and its paramilitary forces of several thousand more personnel overwhelmed the latter, surprising them with its ferocity and coordination in the opening hours of battle. Twenty-three Americans died, as did about

125 Panamanian military personnel. Perhaps 200 to 600 Panamanian civilians died as well.

In the Somalia experience, U.S. forces faced ragtag militia opposition. Somali fighters had access to plentiful automatic weapons, rocket-propelled grenades, and mines, but not much more than that, and they were not trained in combined-arms or coordinated military operations. As is well known, the United States had 18 soldiers killed in action on the night of October 3-4, 1993 in the course of a raid on a building where leaders of the Aideed faction were meeting. The tragedy occurred when two helicopters were shot down by rocket-propelled grenades; additional American casualties were suffered in the effort to rescue any of the crew members that might have survived those crashes. Only about 2,000 U.S. forces were deployed for conducting and supporting such raids at the time they occurred; only 160 participated in the October raid. Estimates of Somali militia strength were in the many thousands, with losses on October 3-4 alone estimated at 300 or more combatants. Often forgotten is that a number of other American troops died in Somalia. In fact, total losses reached 29 from hostile action and 14 from "nonhostile" action such as accidents.

What do past cases tell us about how a future war conducted largely in the streets of Baghdad might play out? As discussed in the link, two useful parallels are the U.S. experience in Mogadishu in 1993 and the U.S. invasion of Panama in 1989. Iraqi forces are almost surely better armed and better trained than the military or paramilitary organizations we fought in those cases. Thankfully, they are probably also far less motivated.

That said, it is important to remember that the Iraqi Republican Guard forces fought reasonably hard in Desert Storm. They also enjoy a number of benefits from Saddam's regime and they are rather heavily implicated in his rule. They would probably fear retribution from an alternative regime or from western occupying forces much more than they would fear Iraqi opposition forces and American airpower on the battlefield. How much they would fear American invasion forces, and thus when they would choose to surrender, is difficult to determine. Whether they could be convinced to desert Saddam by an amnesty offer or a promise of protection and inclusion in a post-Saddam regime is an open question. Whether Saddam's commanders could be deterred from using weapons of mass destruction by threatening to hold them personally responsible should they do so is also unclear.

Simply scaling the results of Panama for the size of the Iraqi military leads to an estimate of about 2,000 killed Americans, more than 10,000 dead Iraqi military personnel, and tens of thousands of dead Iraqi citizens. If however it is only the elite Iraqi forces that fight hard, numbering somewhat more than 100,000 Republican Guard, Special Republican Guard, and palace guard forces, extrapolation from the Panama case suggests that losses on all sides might be only one-fourth as great.

The Somalia analogy is also worth invoking. The firefight on the night of October 3-4 can be used as a way to generate pessimistic estimates of how war in Baghdad might