By Peter Eisler, USA TODAY

The evolution of IEDs in Iraq parallels the evolution of the tools the
Pentagon has used to combat them. The placement of the IEDs, the ways they're triggered, the explosives they employ — all of that has changed time and again as U.S. forces have tried different ways to detect, disable or protect themselves against the devices.

Much of the raw material used by insurgents to make IEDs — artillery shells and explosives, such as TNT and C-4 — was looted from Iraqi military ammunition caches that were not secured by U.S. forces immediately after the invasion, according to a March report by the Government Accountability Office, Congress' investigative arm.

"Not securing these conventional munitions storage sites has been costly," the GAO wrote. The looted material has given insurgents ammunition to "construct IEDs … and maintain the level of violence."

Early IEDs were relatively small and straightforward, often a 155mm or 152mm artillery shell hidden in a wall or embankment along a road. Insurgents would run wire from the device to a handheld trigger, which they could activate from a nearby hiding place.

As U.S. troops figured out how to detect those IEDs, by spotting the wires or a suspicious character nearby, insurgents began using remote triggers — car key fobs, garage door openers, cellphones — to detonate the devices from greater distances. They also turned to more powerful explosives, sometimes "daisy chaining" multiple artillery rounds to boost destructive force.

By March 2004, "they were using daisy chains, 155 mm rounds, maybe seven, eight in a row," says Army Maj. Myles Caggins, who led a support company in Diyala province. "And they had a little ruse: One IED blows up, everyone stops, and as people walk up to investigate, more blow up. The techniques changed."

In late 2003, as troops scoured Iraqi scrap yards for steel to fashion "hillbilly armor" for Humvees, the Pentagon began ordering add-on armor kits for the vehicles, including hardened steel doors and side panels. By May 2004, under pressure from Congress, the Army had delivered 7,000 kits; more arrived in the months that followed.

Around that time, troops also started getting their first large-scale deliveries of jammers: devices that can be mounted in a vehicle or, in some cases, carried in a backpack, to block the wireless signals insurgents used to set off IEDs.

The insurgents adapted faster.

By early 2004, they'd begun burying IEDs under roads, so they would blast up through the thin floors that proved to be the Achilles' heel of even the armored Humvees. And the use of those buried IEDs grew steadily over the next 18 months, as more armored Humvees reached the field.

The triggers changed, too. As more jammers arrived, insurgents reverted to hard-wired devices or switched to pressure-plate IEDs, which go off when a vehicle rolls over them. By 2006, U.S. troops were seeing "baking trays," in which C-4 is sandwiched between metal plates and set to explode when compressed by a vehicle.

"They have adapted every time we've come up with a new way to defeat them," says Rep. John Murtha, D-Pa., a combat veteran and critic of the war.

Now, they're adapting again, using IEDs that employ "explosively formed projectiles," known as EFPs. Those devices fire a metal slug that becomes a molten projectile as it travels towards its target. They are so powerful that they've been described as capable of slicing through an Abrams tank.

The Pentagon is developing yet another armor kit — this time to put on already armored vehicles, including MRAPs and Humvees — that can protect against EFPs.

From the start, the insurgents "made a decision to attack our tactical mobility … and they've chosen the IED as the way to do that," says retired Marine general Anthony Zinni, former chief of the U.S. Central Command. "This is the first war where we've faced an enemy that's adapted better than we have at a tactical and operational level. We had IEDs from Day 1. … What have we done to adapt? Nothing