The first part of April has been the bloodiest period so far for U.S. troops in Iraq. There were 87 deaths by hostile fire in the first 15 days of this month, more than in the opening two weeks of the invasion, when 82 Americans were killed in action.

There are 135,000 U.S. troops in Iraq. Nearly 700 American troops have died since the beginning of the war. As of Friday, 493 had been killed by hostile fire.

The Vietnam War started with a slower death rate. The United States had been involved in Vietnam for six years before total fatalities surpassed 500 in 1965, the year President Lyndon B. Johnson ordered a massive buildup of forces. There were 20,000 troops in Vietnam by the end of 1964. There were more than 200,000 a year later.

By the end of 1966, U.S. combat deaths in Vietnam had reached 3,910. By 1968, the peak of U.S. involvement, there were more than 500,000 troops in the country.

Senior U.S. officials insist the current fighting is only a "spike" and not indicative of a widening war. On Thursday, Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, described the current fighting as a "symptom of the success" U.S. forces are having in Iraq.

Gunfire has been the biggest killer of U.S. troops, followed closely by improvised explosive devices. The two account for more than 250 deaths.

Those killed represent a wide range of military specialties. Truck drivers and clerks are getting killed just as often, if not more often, than infantrymen and other combat specialties.

The average age of a casualty in Vietnam was 20 years old. The average age of a casualty in Iraq is nearly 27. More than 12 percent of those killed have come from the Army National Guard and Army Reserve, which helps explain why the average age of the dead is higher.

The dead were from all 50 states, plus the District of Columbia, Puerto Rico, American Samoa and the Marianas, a U.S. protectorate.

Nearly 70 percent were white, according to Pentagon figures from April 8, the last date for which those statistics were available. Twelve percent were Hispanic, and 14 percent were black. Asians and other races accounted for less than 6 percent.

Many of those killed were from small towns and inner cities, rather than the suburbs, Moskos said.

Hostile fire has accounted for about 70 percent of the deaths in Iraq,

In all, 88 U.S. troops died in the first 15 days of April, including one whose death wasn't caused by hostile fire. In the first two weeks of the war, 98 died, including 16 from non-hostile causes.