7 Marines Dead in Explosion at Nev. Army Depot Another 8 wounded during training exercise accident By Evann Gastaldo, Newser Staff Posted Mar 19, 2013 7:58 AM CDT Updated Mar 19, 2013 8:20 AM CDT 4 comments Comments Soldiers from Operational Detachment Alpha 3133 conduct a mounted-dismounted route clearing exercise during a pre-mission training exercise at the Hawthorne, Nev., Army Depot on Oct. 6, 2008. (AP Photo/U.S. Army, Staff Sgt. Corey T. Dennis) (Newser) – Seven US Marines are dead after an explosion at Hawthorne Army Depot in Nevada last night, military officials tell NBC News. The accident occurred at an ammunition storage facility during a live-fire training exercise, when a 60-millimeter mortar exploded in a tube as Marines were getting ready to fire it. Another eight Marines were wounded; three are in serious condition. The 147,000-acre depot is used for storing and destroying demilitarized ammo, Reuters reports.