For the 160 national guardsmen from America's heartland, Baghdad was more than just a long way from home. It also confronted the 233rd Military Police Company with America's most difficult challenge in Iraq: establishing security in a nation rife with religious, tribal, and sectarian conflict and violence.

The first MP company assigned to patrol the heart of Baghdad, the 233rd (from Springfield, Illinois) was a key part of the American occupation forces from April 2003 to April 2004. Charged with helping rebuild the city's police force-not just reopening stations but training a new force...