At Camp Victory outside Baghdad, 1,215 troops from the Army, Marines, and other services reenlisted in a mass swearing-in ceremony led by General David Petraeus, the top war commander.
At least two husband-and-wife couples were among those signing up for another military stint.
In front of an immense American flag hung in the rotunda of the palace headquarters of the US military in Iraq, the troops saluted Petraeus, then sang "God Bless America."
In new violence across Iraq yesterday, gunmen on a motorcycle assassinated an official of Iraq's largest Shi'ite party in the southern city of Basra, police said.
Sheik Salim al-Dirraji was gunned down in the Hayania district, which had been a stronghold of the Mahdi Army of radical cleric Moqtada al-Sadr until a security crackdown last spring.
Dirraji was a local official of the Supreme Islamic Iraqi Council, the leading rival of Sadr's party within the Shi'ite community.
The holiday celebrations for US troops were leaner at smaller outposts closer to the violence. There it meant a can of meat and some cookies.
"We are not going to stop our operations to celebrate the Fourth of July," said Sergeant Mark Johnson, 26, at a small joint US-Iraqi outpost in the city of Iskandariyah, some 30 miles south of Baghdad.
"Nothing special is planned for today, and that's OK because we didn't expect anything," added the Third Infantry Division soldier from Waterport, N.Y.
It was quiet yesterday at the Iskandariyah outpost, giving the men who weren't on duty time to watch movies on their laptops and exchange instant messages with friends back home.
"The holidays are not important," said First Lieutenant William Kuebler, 24, of Moville, Iowa, a member of the 101st Airborne Division.
Things were a bit more festive at Forward Operating Base Warhorse in Baqubah, 35 miles northeast of Baghdad. There was a special menu in the chow hall and a three-on-three basketball tournament in which Covarrubias took part.
Before hitting the court, Covarrubias, of the Second Stryker Cavalry Regiment, planned to call his relatives.
Although he misses his family, the 29-year-old from Hawthorne, Calif., said the holiday still made him feel good.
"For me, on the Fourth of July, you remember there's people out there that think about you out here," he said.
Sergeant Jacob Fultz, 22, of Gardner, Kan., also assigned to Warhorse, focused on the day's meaning.
"It's kind of like the fight's never over," Fultz said. "It started on July 4, 1776, and now it's 2008."
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