Fifteen rifles stood in a row with their barrels down, each topped by a U.S. military helmet and framed by an empty pair of combat boots.

In the middle of a parched athletic field at this dusty desert camp, an officer with the 3rd Armored Cavalry Regiment (search) read 15 names in a solemn roll call Thursday. The only response was silence.

About 1,000 U.S. soldiers, some wearing spurs and black regimental hats from the Indian Wars of the Old West, gathered at the regiment's western Iraq headquarters to remember 15 comrades who died last weekend in the worst single attack against U.S. forces since the war began.

"Death was in the cause of freedom. They were serving our country and answering our nation's call to fight terrorists," said Col. David A. Teeples, commander of the regiment from Fort Carson (search), Colo.

"We honor them for their sacrifice. We honor them as Americans, as soldiers and as family."

In the hours after the ceremony, another soldier died from wounds suffered in the crash, bringing the death toll to 16.

The official count of the wounded had been 21 prior to the latest death. However, the U.S. Defense Department said in a statement later Thursday that 26 soldiers were recovering from their wounds. The statement did not elaborate.

On Sunday, guerrillas near Fallujah shot down one of two U.S. Army Chinook helicopters flying dozens of soldiers to Baghdad International Airport (search). From Baghdad, they were scheduled to fly home on leave.

The attack underscored the growing resistance to the U.S.-led occupation. The insurgency has gradually spread through much of the Sunni Muslim areas in the center and north of the country.

Following the ceremony at the base 200 miles northwest of Baghdad, Teeples said there had been no reduction in helicopter flights since Sunday but "some adjustments" were made in times and flight paths.

"The troops remain mission-oriented and they do realize that they are in a high-stress combat area," Teeples said. "They are confident in their equipment and their training."

Near the end of Thursday's solemn ceremony, Command Sgt. Maj. John R. Caldwell called the roll, reading out the names and ranks of all 15 victims -- 13 men and two women.

As cavalry units sometime do for formal ceremonies, many of the assembled soldiers wore black cavalry hats dating to the 19th century, with spurs attached to their combat boots.

The 30-minute ceremony featured a rendition of "America the Beautiful" and a reading of Psalm 23 from the Bible, which says in part, "Yea, though I walk through the valley of the shadow of death/I will fear no evil."

The service ended when Spc. Valerie Hills, of Grayson, La., sang "Amazing Grace," and a squad of soldiers fired three volleys into the night sky. Two combat helicopters then flew overhead.

Sgt. Charles Elliott, 43, reservist from Neodesha, Kan., said he was on a second Chinook that was flying in formation with the one that was hit.

They landed immediately after the crash, and the 22 people on board rushed out to help the injured.

"It did not look like a helicopter. I'd never seen anything that bad," Elliott said.

Despite the shock of seeing so many fellow soldiers dead or severely injured, Elliott, a fireman in civilian life who is serving in the 323rd Engineer Detachment, said he was determined to remain focused on his work.

"My intention is to do my job and to do my job well, and if I do then I won't have to come to many of these."

The regimental chaplain Maj. Christopher Faria said individual memorial services already had been held before the collective one.

"There is a lot of anger and shock at what happened, and with this memorial service we are trying to provide a channel for the grief," Faria said.