RENO, Nev. —
The Marine Corps official said an explosion at the point of firing in a training exercise could kill or maim anyone inside or nearby the protective mortar pit and could concussively detonate any mortars stored nearby in a phenomenon known as "sympathetic detonation."
The official did not know whether the seven dead Marines and several others who were hurt were in the same firing pit, standing nearby for training observation or in an adjoining mortar pit, but any of those situations would have been them in danger after such an explosion.
The official said a worldwide moratorium after such an accident is not unusual and would persist until the investigation determines that the weapon did not malfunction in ways that would hurt other Marines or that mortars manufactured at the same time as the one involved in the accident were safe to continue to use.
The official said it would be normal to warn other U.S. military branches that use 60mm mortars, such as the Army, about the Marines warning. The moratorium could last for weeks or months.
The investigation will focus on whether the Marines followed procedures to properly fire the weapon, whether there was a malfunction in the firing device or in the explosive mortar itself, the official said.
The Hawthorne Army Depot stores and disposes of ammunition. The facility is made up of hundreds of buildings spread over more than 230 square miles.
Hawthorne has held an important place in American military history since World War II when it became the staging area for ammunition, bombs and rockets for the war. The Nevada Division of Environmental Protection says that the depot employed more than 5,500 people at its peak. Nevada was chosen for the location because of its remoteness in the wake of a devastating explosion at the government's main depot in New Jersey in the 1920s.