The M4 rifle is the main weapon of American soldiers fighting in Iraq and Afghanistan, with more than 500,000 in service. Although the vast majority of soldiers are said to have no problems with the weapon, the M4 proved unreliable in a deadly firefight July 13, 2008, in Wanat, Afghanistan, where nine U.S. soldiers were killed. One review of the battle found some of the rifles failed at a “critical moment,” adding to a growing minority of complaints by soldiers that the M4 jams too often and requires too much maintenance.