A University of Pennsylvania report, titled Mortality of American Troops in Iraq, breaks down American casualties by many different demographics. One statistic that hits close to home for me is the disparity between Marines and other branches. The Marine Corps death rate in Iraq is more than doubled that of the Army, and ten times higher than that of the Navy and Air Force.
This is due to the heavy Marine Corps presence in the most volatile area of Iraq, the al Anbar province, which includes the cities of Fallujah, Haditha and Ramadi. Major battles in both Fallujah and Ramadi, particularly the Second Battle of Fallujah, are considered to have been the heaviest fighting American forces encountered during the entire war.
Source: University of Pennsylvania