WASHINGTON -- Despite a determined Defense Department effort to protect troops from deadly roadside bombs, the toll in Iraq continues to rise, with at least 19 American servicemen killed in the past week when insurgents' bombs tore their vehicles.
Since the war began four years ago, Pentagon officials acknowledge, more than 2,000 U.S. troops have been killed and about 18,000 wounded when improvised bombs have shattered even heavily armored Humvees and other vehicles in Iraq and Afghanistan.
American forces have recorded successes, finding and disabling or destroying many roadside bombs before they explode, U.S. officials said. Tips from Iraqis about hidden bombs have more than doubled since August, rising from 4,250 that month to 10,070 in January, defense officials said.
This work has paid off. Only one in five roadside bomb incidents involves a detonation that causes American casualties, according to Montgomery C. Meigs, the retired Army general who heads the Pentagon's $4.4 billion campaign against roadside bombs.
But even this all-out effort has been unable to stop the steady killing and wounding of American troops, raising questions of whether the United States can impose security across Iraq and, ultimately, its ability to prevail against low-tech insurgents in future conflicts.
Amid an intensifying war - exemplified by the deadly suicide bomb attacks yesterday that killed 106 Shiite pilgrims in southern Iraq - analysts said it is likely that American casualties from roadside bombs will continue, despite the "surge" of about 27,000 more U.S. troops.
"The good news is that the rate of U.S. casualties has not gone up, even though the number of explosions has increased greatly," said Loren Thompson, a defense expert at the Lexington Institute, a nonpartisan think tank in Washington. "The bad news is that the rate of casualties has not gone down, even though we are spending billions of dollars and millions of man-hours just to stop them from increasing.
"If an inferior force is hurting you in ways you are unable to prevent, you are losing," he said.
Insurgents in Iraq have mastered two forms of assault that have proven tragically difficult for U.S. forces to prevent. One is the suicide attack, with a bomb strapped to a person's chest or packed into a car. The other is the improvised explosive device, or IED, built from land mines, artillery shells, mortar rounds and rockets, sometimes wired together and buried in roadways or hidden beside them. Most of the munitions made into IEDs came from Iraqi weapons stores left unguarded after the U.S.-led invasion in March 2003, according to the Government Accountability Office, the investigative arm of Congress.
More deadly forms of IEDS are shaped charges that can penetrate the heaviest U.S. armor. These "explosively formed penetrators," or EFPs, are simple but effective devices from Iran, U.S. officials have said.
Although suicide bombers have attacked U.S. military convoys, they more often target Iraqis. IED attacks are aimed mostly at American forces.
Senior officials expressed frustration that despite the best American technology, insurgent bomb-makers seem able to stay a step ahead. When U.S. troops got good at spotting wires used to detonate IEDs, for instance, insurgents began using remote-control devices. When the Pentagon developed and fielded thousands of sophisticated jammers, insurgents went back to wires.
When the Pentagon added armor to Humvees, insurgents built more powerful bombs.
"The reality is, we face an agile and a smart adversary," Defense Secretary Robert M. Gates told a congressional committee last week. "As soon as we ... find one way of trying to thwart their efforts, they find a technology or a new way of going about their business.
"The most unpleasant aspect of my job is every night going home and hand-writing notes to the families of those who have been killed in action. And there's a sheet behind every one of those letters that tells me how they died, and about 70 percent of them are the IEDs," Gates said. "So, the whole Department of Defense is as highly motivated as an organization can be to try and figure out a way to get around these."
Inevitably, though, the U.S. response to a new or more powerful form of IED is slow and expensive. The Marine Corps concluded last month that even heavily armored Humvees are vulnerable. At the request of Lt. Gen. James N. Mattis, the service's commander in the Middle East, Marine Humvees in Iraq will be replaced with new mine-resistant, ambush-protected armored vehicles, or MRAPs, which have a V-shaped hull to deflect the blast of an IED and cost up to $700,000 each.
Army and Marine units now have 465 of the vehicles in Iraq. More are in production and will begin to be shipped next month. A new class of MRAP prototypes is arriving at the Army's Aberdeen Test Center in Maryland. Those selected for production won't be delivered until 2008.
Altogether, the two services plan to deploy more than 4,000 MRAP vehicles, such an expense that the Army has been unable to budget the $2.2 billion it will cost for its share of the vehicles.
A more effective replacement for the Humvee won't be available at least until 2012, Army officials say.
For the Pentagon, the problem isn't just the enormous cost of responding to a weapon built from cast-off munitions and cheap electronics, such as garage door openers. The problem is also the time it takes to respond.
"As long as the insurgents have a certain level of technical skill, it probably isn't realistic to think that we can react faster than they can innovate," Thompson said. "But unless we can react faster, there is no way to defeat this threat."
Faced with such problems, the Pentagon's IED task force has begun to shift attention to identifying and penetrating the insurgent networks responsible for such attacks. The effort requires painstaking work by intelligence and explosives experts to identify bomb-makers and track insurgents who plant the devices.
Pentagon officials declined to discuss the work.
Meigs said he is more than doubling the money put into penetrating and destroying IED networks, an effort recognized by President Bush during a speech yesterday to the American Legion.
"In the past two weeks, U.S. and Iraqi forces have also uncovered large stockpiles of explosively formed projectiles, or EFPs, which are used by extremist groups to attack our troops," Bush said. "Iraqi and U.S. forces are making gradual but important progress almost every day, and we will remain steadfast until our objectives are achieved."