'The IED problem is getting out of control. We've got to stop the bleeding.'

By the early fall of 2003, IED attacks had reached 100 a month, according to a House Armed Services Committee document. Most were a nuisance; some proved stunning and murderous. A large explosion along a roadbed near Balad in October of that year flung a 70-ton M1A2 Abrams tank down an embankment, shearing off the turret and killing two crewmen. Even more horrifying was a truck bomb at 4:45 p.m. on Aug. 19 that demolished the United Nations headquarters in Baghdad, killing the U.N. special representative and 22 others.

Day by day, as Adamson would write, "the concept of a front, or line of battle, vanished" in Iraq, giving way to "360-degree warfare."

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IEDs had quickly moved to the top of Abizaid's anxieties at Central Command. A Lebanese American who spoke Arabic and who had studied as an Olmsted scholar at the University of Jordan in Amman, the four-star general had seen for himself the aggravation that roadside bombs caused Israeli forces in Lebanon in the 1980s.

Two weeks after taking command from the retiring Gen. Tommy R. Franks, Abizaid publicly described resistance in Iraq as "a classical guerrilla-style campaign," a blunt appraisal that reportedly irked the Pentagon's civilian leadership. But the amount of unsecured ammunition in Iraq, particularly in Sunni regions, alarmed him. So did the realization that many Iraqi military officers -- unemployed and disgruntled after the national army was disbanded in late May -- possessed extensive skill in handling explosives.

Abizaid hoped that American technical savvy would produce a gadget that could detect bombs at a distance, "a scientific molecular sniffer, or something," as he put it. "We thought the problem would spread," Abizaid later reflected, "but it didn't appear overly sophisticated." Underestimating the enemy's creativity and overestimating American ingenuity, a pattern established before the war began, continued long after the capture of Baghdad.

Lt. Gen. Ricardo S. Sanchez, the senior U.S. ground commander in Iraq, told Pentagon strategists that he hoped to minimize the military's "footprint" in Iraq by maintaining an occupation force that was two-thirds motorized and only one-third mechanized. "What I don't want is a lot of tanks and Bradleys," Sanchez said, according to a senior Army commander.

That meant mounting most troops on Humvees, few of which were built to withstand bombs or even small-arms fire. Soldiers had begun fashioning crude "hillbilly armor" for their vehicles from scrap metal. Even factory-built armored vehicles had been designed to resist projectiles fired at a distance, according to a senior Army scientist, and not against point-blank explosions in which steel fragments and blast overpressure -- from gases hotter than 3,000 degrees Fahrenheit forming in 1/10,000th of a second -- struck simultaneously.

Production of the stout "uparmored" Humvee started in 1996, but as a specialty vehicle for military police and Special Forces; an average of one per day had been built before the war, according to congressional documents. The entire fleet of uparmored Humvees in the theater in 2003 totaled 235, the Army chief of staff would later report.

With no master list of where uparmored Humvees were deployed, logisticians searched U.S. motor pools around the world. Seventy were found in Air Force missile fields in North Dakota and elsewhere, according to a former senior officer on the joint staff, but it took a four-star order to pry them away for duty in the Middle East.

Protecting individual soldiers was a bit simpler. In June 2003, the Pentagon decided to outfit every trooper in theater with tough interceptor body armor. By December, eight vendors would produce 25,000 sets a month, according to congressional documents, and by April 2004 all U.S. military personnel in Iraq had received high-quality protection. The documents show that Congress has appropriated more than $4 billion for body armor so far.

But as summer yielded to fall in 2003, the final defense against roadside bombs often fell to a few hundred EOD technicians, whose informal motto -- "Initial success or total failure" -- suggested the hazards in what was known as "the long walk."