Many of the troops are serving multiple tours in Iraq.

He went on to serve three tours of duty in Vietnam.

He served two tours of duty in Vietnam, 1965-1966 and 1969-1970.

In exchange for this, they served tours as base guards.

Even given these conditions, the men were expected to serve three-year tours of duty.

Many of the troops have served multiple tours in Iraq and are weary.

He served three tours of duty in Vietnam, two as executive officer.

About half of the 32,000 marines now stationed in Iraq are serving second tours, he said.

They may serve tours as instructors, or on various staffs.

But he volunteered for the mission so other soldiers who had served multiple tours in Iraq could get a rest, she said.