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

If no one foresaw that within four years more than 30,000 jammers of all sorts would be in Iraq, a few suspected that something big had started. "We're going to need a lot more jammers," Col. Bruce Jette, who commanded the Army's Rapid Equipping Force at Fort Belvoir, told a Fort Monmouth engineer in August 2003. "And eventually we're going to need a jammer on every vehicle."

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Bombmaking by definition required explosives, and in that commodity, as in oil, Iraq was richly endowed. "The entire country was one big ammo dump," Defense Secretary Robert M. Gates would observe this past March. "It's just a huge, huge problem."

The problem was also huge in 2003. Yet U.S. strategists, who before the invasion failed to anticipate an insurgency, also drafted no comprehensive plans for securing thousands of munitions caches, now estimated to have held at least 650,000 tons and perhaps more than 1 million tons of explosives. "There's more ammunition in Iraq than any place I've ever been in my life, and it's not securable," Gen. John P. Abizaid told the Senate Appropriations Committee shortly after taking over U.S. Central Command in July 2003. "I wish I could tell you that we had it all under control. We don't."

To forestall looting, U.S. forces tried spreading putrid substances across the dumps, as well as cementing artillery rounds together or burying large caches. "We're now finding people tunneling 30 feet down and carting the stuff away," an analyst noted earlier this year. Sloshing diesel fuel across the dumps and lighting it, among several haphazard "blow and go" techniques, often simply scattered the rounds. More than a year after the invasion "only 40 percent of Iraq's pre-war munitions inventory was secured or destroyed," the Congressional Research Service reported this summer.

Tens of thousands of tons probably were pilfered, U.S. government analysts believe. (If properly positioned, 20 pounds of high explosive can destroy any vehicle the Army owns.) The lax control would continue long after Hussein was routed: 10,000 or more blasting caps -- also vital to bombmaking -- vanished from an Iraqi bureau of mines storage facility in 2004, along with "thousands of kilometers" of detonation cord, according to a Defense Intelligence Agency analyst.

In the summer of 2003, pilfered explosives appeared in growing numbers of IEDs. Main Supply Route Tampa, the main road for military convoys driving between Baghdad and Kuwait, became a common target. Three artillery shells wired to a timer west of Taji, discovered on July 29, reportedly made up the first confirmed delay bomb. Others were soon found using egg timers or Chinese washing-machine timers.

Radio-controlled triggers tended to be simple and low-power, using car key fobs or wireless doorbell buzzers -- Qusun was the most common brand -- with a range of 200 meters or less. Radio controls from toy cars beamed signals to a small electrical motor attached to a bomb detonator; turning the toy's front wheels completed the circuit and triggered the explosion.

U.S. troops dubbed the crude devices "bang-bang" because spurious signals could cause premature detonations, sometimes killing the emplacer. Bombers soon learned to install safety switches in the contraptions, and to use better radio links.

Camouflage remained simple, with bombs tucked in roadkill or behind highway guardrails. (Soldiers soon ripped out hundreds of miles of guardrail.) Emplacers often used the same "blow hole" repeatedly, returning to familiar roadside "hot spots" again and again. But early in the insurgency, before U.S. troops were better trained, only about one bomb in 10 was found and neutralized, according to an Army colonel.

Coalition forces tended to concentrate at large FOBs -- forward operating bases -- with few entry roads. "Insurgents seized the initiative on these common routes," according to a 2007 account of the counter-IED effort by Col. William G. Adamson. "The vast majority of IED attacks occurred within a short distance of the FOBs."

Each week, the cat-and-mouse game expanded. When coalition convoys routinely began stopping 300 yards from a suspected IED, insurgents planted easily spotted hoax bombs to halt traffic, then detonated explosives that had been hidden where a convoy would most likely pull over.