The looming conflict with Iraq catches many senior leaders of U.S. ground forces in an awkward position: one foot in the future, one in the past, and passionately separated from the civilian leaders whose authority they accept but whose military judgment they do not always respect.
As a result, the U.S. battle plan for invading Iraq reflects an uneasy compromise between civilian leaders who put their faith in new strategies and technologies and ground commanders who believe that the underlying realities of war do not change.
The sometimes bitter debate has haunted the planning of military action against Iraqi leader Saddam Hussein for more than a year.
The dispute has focused on how important a role to assign to armor and heavy infantry -- the 70-ton Abrams tanks used by the Army and the Marines, the armor-plated Bradley fighting vehicles, the mechanized artillery, the tank-killing helicopters and the vast supply train needed to keep them rolling.
On one side are Defense Secretary Donald H. Rumsfeld and some of his closest aides, who consider the armed forces -- especially the Army -- too slow, too heavy and too inflexible to meet the challenges of the post-Cold War world.
Rumsfeld and his inner circle want what he once called "new ways of thinking, and new ways of fighting." That translates into greater reliance on high-tech weapons, especially air power, and on the light, fast-moving capabilities of special operations forces who won a quick, low-cost victory in Afghanistan.
In this view, the nature of the threat has fundamentally changed since the Cold War ended and the United States became the world's only superpower. Instead of conventional armies, the nation would now face unconventional forces using tactics that avoid head-on confrontations with U.S. power.
On the other side are many of the senior leaders of the Army and other ground forces. They, too, favor "transformation" to a lighter, more agile force, but they insist that this force must retain the overwhelming battlefield superiority of today's heavy ground units.
And, they have argued, until such new capabilities arrive -- sometime in the next decade -- there is a vital role for the tank brigades and heavy infantry designed decades ago for a war against the Soviet Union.
These military leaders say Iraq and other potential adversaries possess enough tanks and other conventional forces to threaten all but the strongest American units. They see over-reliance on Special Forces troops and other so-called "light" units as a dangerous infatuation.
"I thought it was the generals who always fought the last war," a senior general said recently, referring to the "light infantry" tactics used in Afghanistan and expressing frustration with what he considered "the one-dimensionality" of some civilian leaders' thinking.
Although the United States will ultimately prevail, the commanders believe, things always go wrong in the chaos of war. There is no such thing as victory on the cheap. The only sensible approach is to mobilize the strongest force possible, backed by maximum support to cope with the inevitable mishaps.
"These people believe in perfection," a senior ground commander declared several months ago, giving vent to the frustration he felt in dealing with the Pentagon's senior leadership. "They believe 'surgical' is possible. We don't."
The dispute has churned beneath the surface in Pentagon conference rooms, obscure military journals and little-noticed skirmishes over military budgets. It came to a head last year as the Pentagon planned for war with Iraq.
For months last summer and through the fall, Rumsfeld and his senior aides challenged plans for the kind of massive buildup of troops and materiel that characterized the 1991 Persian Gulf War.
Why, senior officials asked, did ground commanders need so many troops, so much heavy equipment, such mountains of supplies? Why couldn't the planners be more imaginative? Why couldn't they do the job with surgical applications of air power and the fast-moving, light and flexible tactics of the Afghanistan war?
The answer, senior Army leaders said, is that "going heavy" with the forces that many civilian Pentagon officials consider outmoded would ultimately promote a quicker, cleaner victory at lower cost in American and Iraqi lives -- even if a U.S. invasion leads to warfare in the streets of Baghdad.
"That's a force no one in the world can stand against," said Lt. Gen. John M. Riggs, who heads the Army's effort to develop new war fighting systems but considers the heavy forces developed in the Cold War indispensable for now.
To be sure, some analysts believe that a U.S. invasion could end almost before it begins. Sensing imminent defeat, Hussein's lieutenants might turn on him in the first hours of war. Regular Iraqi troops might surrender en masse. Or, as happened in 1991, air power could shatter Iraqi military units before they can engage U.S. ground forces, turning the war into a rout.
If things turn out that way, Army leaders say, fine. But what if some U.S. units run into unexpected trouble? Suppose Iraqis, pushed to the wall on their home ground, decide to fight -- as poorly armed but enraged civilians did in the streets of Mogadishu, Somalia, a decade ago?
In such situations, armor and other heavy forces could be all that stands between lightly armed U.S. units and disaster.
Moreover, using the armed forces' most powerful ground units reduces the likelihood of protracted battles and actually gives planners more freedom to use the light forces in imaginative ways.
Admittedly, refueling, resupply and other logistical support for today's forces require a long and massive buildup; the M1A1 Abrams tank eats five gallons of special diesel fuel or more per mile under combat conditions.
The appetite for ammunition and -- especially in the desert -- water is equally gargantuan.
Keeping an armored column rolling requires a complex ballet of support units. Hundreds of off-road fuel tankers, ammunition trucks and other specialized vehicles shuttle continuously between the lead elements of the attack and supply points that can be many miles to the rear.
Getting such a force into position takes months and billions of dollars. Its enormous footprint aggravates political and diplomatic problems for potential allies.
What heavy forces deliver in return is irresistible firepower, speed and combat superiority against anything Iraq can muster. They can drive forward with around-the-clock assaults, giving enemy commanders little time to regroup, counterattack or bog down U.S. forces in extended, potentially bloody engagements.
And, backed by armor and mechanized infantry, airborne units can "leap-frog" over Iraqi lines and seize key objectives.
Such large-scale "vertical envelopment" is expected to be a major -- and spectacular -- innovation in a war with Iraq, permitting allied forces to throw Baghdad's defenses into chaos and capture oil fields, river crossings and other targets in the opening hours of a conflict.
But the key to using such tactics safely, ground commanders say, is having sufficient heavy forces to drive into Iraq and reinforce the Special Forces, Rangers and other light units before Iraq can counterattack with more heavily armed forces.
Light forces "have great mobility, but their protection and firepower are not what you'd like them to be," said an Army colonel with broad knowledge of both kinds of forces. "Light forces are vulnerable to heavy forces."
In the end, the Pentagon settled on a war plan that includes more heavy forces than Rumsfeld initially wanted but also envisions bold strokes by Special Forces and large-scale use of air-mobile light infantry.
Although Iraq's military capabilities have eroded since 1991, it retains significant quantities of armor and artillery.
One U.S. field commander, for example, says intelligence reports indicate that the Iraqis recently augmented their forces with 300 Russian-made T-72 tanks, apparently supplied through Syria.
These tanks would be no match for the Army's M1A1 and M1A2 Abrams main battle tanks, with their supporting phalanx of Bradleys, artillery, tank-killing gunships and fixed-wing aircraft.
The M1's 120-millimeter main gun can shoot farther and score first-shot kills more often than Iraqi tanks. U.S. tanks also have long-range thermal sights that can penetrate smoke, fog, dust and darkness.
One major advantage of the Abrams, Army officials say, is that it fires depleted uranium rounds that bore through armor plating. Still, reflecting the fatalism that is bred in their bones, ground combat officers return to the thought that in war, nothing is certain.
"Even if the Iraqi army is not a well-trained army, the equipment that they have can bring a lot of harm to my solders," said Lt. Col. Stephen Twitty, a battalion commander in Kuwait.