TIKRIT, Iraq — Sgt. 1st Class Dale Toomey slipped his iPod buds under his radio headset and cautioned the rookie driver and gunner about potholes, parked cars and pedestrians as the Humvee convoy entered Tikrit.

"Keep an eye on this guy walking on the left," Toomey, of Gastonia, N.C., barked to the 18-year-old gunner. "Keep moving left and right, up and down. Don't be a silhouette."

As a veteran of the 505th Engineering Battalion, Toomey, 37, and fellow National Guard members from the greater Charlotte, N.C., area were showing their replacements what it's like to drive the insurgent-infested, Tikrit-to-Baghdad highway.

Since U.S. forces have massed in the capital to suppress sectarian violence in recent weeks, insurgent bombings have increased to the west in the Anbar province and to the north, closer to Tikrit.

Toomey, seated in the fourth of the five-vehicle caravan, set his iPod to Tim McGraw. Then, at 10:03 a.m. Iraq time, BOOM!

An explosive hidden in the median rocked the Humvee, the fourth in the five-vehicle caravan. The fifth and last vehicle bore the brunt of the blast.

"IED! IED! IED!" Toomey shouted over the radio. An improvised explosive device had gone off.

Toomey grabbed a handful of gunner Richard Malloy's trousers and yanked him to the floor. The young soldier pressed his hands against his Kevlar helmet and buried his head between his knees. Off in the distance, the thump, thump, thump of a firefight between U.S. forces and insurgents heightened the chaos.

"We've got one, maybe two flat tires!" the fifth driver, Staff Sgt. Don Chandler, 38, of Silver Grove, Ky., called out. "We're still moving."

The fifth Humvee took the fourth spot, as the convoy communicated the extent of the damage. As it passed Toomey, he noted that only the right front tire was damaged. All vehicles kept rolling. A small roadside base was about a mile away.

"It can ride on the rim if it has to," Toomey said nonchalantly, quickly turning his attention to Malloy, who had returned topside to man his M-249 belt-fed machine gun. "Sorry I jerked your pants down."

CHANGING DUTIES

With regular military stretched thin, the Pentagon has leaned on a massive deployment of citizen soldiers from National Guard and Reserve units for its mission in Iraq.

The 505th Battalion of the North Carolina National Guard has been in Iraq for a year. It is about to hand over construction, demolition, road repair and convoy duty to the Army's 19th Engineering Battalion out of Fort Knox, Ky.

The members of the 505th, which has its headquarters in Gastonia, N.C., are returning home in the coming weeks.

Potholes in Charlotte are annoying. Potholes in Iraq can be deadly. They make ideal hiding places for improvised explosive devices. IEDs are responsible for 969 of the 2,682 U.S. deaths in Iraq over the past 3 1/2 years, according to Iraq Coalition Casualty Count, a Web site that tracks military fatalities.

Of some 2,000 convoys the 505th has run in its year in Iraq, less than 3 percent have hit IEDs, said Capt. Kyle Meisner. The numbers look comforting on paper. Inside a Humvee, even an armored one bristling with machine guns and assault rifles, IEDs take on reaperlike meaning.

At the roadside base, the 22 soldiers dismounted and gathered around the damaged Humvee. Many lit cigarettes. Some who didn't smoke stuffed Copenhagen chewing tobacco between their cheek and gum.

One soldier wept.

Each Humvee had at least one member of the 505th along that day. All had experienced an IED while on tour in Iraq.

TRYING TO HELP

A cluster of young soldiers from the 19th Engineering Battalion sought shade in an overhang. Two dogs wagged their tails and made the rounds of the adoring soldiers.

Among them was Thomas Meadows, 19, of Indianapolis, the gunner aboard the fifth Humvee.

The blast had knocked him off his feet and snapped his head back. He thought he may have a concussion.

It was his first time "outside the wire," his first convoy of what will be many in Iraq.

He talked about wanting to be a policeman in Indianapolis and about his wife and about the upcoming birth of their daughter, due in December.

"I just don't understand why they do this when all we're trying to do is help."

Less than two hours after the attack, the convoy was ready to roll again.

Those in charge decided to continue with the mission, rather than return to base. The convoy would press south to Samarra, have lunch at a base, practice closing a road and checking a bridge, then return to Camp Speicher, just outside Tikrit, Saddam Hussein's hometown.

When about some 200 members of the 505th — a quarter of the battalion — arrived last year, the departing unit rode only one, uneventful training mission. That unit had suffered a death by IED, and its commander had a heart attack. So the 505th had to do a lot of on-the-job training.

It has been blessed so far. The 505th has not suffered a fatality.

"I hate to say it, but what happened today was a good thing," Toomey said. "It was a wake-up call. It's for real."

He let the words sink in, as he pondered the reality of IEDs.

"It's not a matter of if," he added. "It's a matter of when."