( CNN ) -- They came from all across America -- from Connecticut to Florida to Illinois and many points in between . One had been in the Marines for nearly four and a half years , another for just a few months . Many served in Afghanistan , earning numerous honors before making it safely back home to the United States . On Wednesday , the military released the names of the seven Marines killed Monday night during a training exercise at Hawthorne Army Depot in western Nevada . 7 killed in explosion at Nevada Marine training exercise . `` Our hearts , thoughts and prayers go out to the families and friends of our fallen angels , '' said Lt. Col. Andrew J. McNulty , commanding officer of the 1st Battalion , 9th Marine Regiment . Those killed are : . • Lance Cpl . David P. Fenn II : The Polk City , Florida , resident joined the Marines in June 2010 and was promoted nine months later . In that time , he 'd deployed to Afghanistan where -- among other honors -- he earned a NATO Medal-ISAF Afghanistan and Afghanistan Campaign Medal . The mortarman was 20 . • Pfc . Joshua M. Martino : The 19-year-old from Clearfield , Pennsylvania , was a mortarman in the regiment . He joined the Marines in July , but already had earned the National Defense Service Medal and Global War on Terrorism Service Medal . • Lance Cpl . Roger W. Muchnick , Jr. : Muchnik , 23 , hailed from the southwestern Connecticut town of Fairfield , and ended up in Afghanistan as a mortarman with the 1st Battalion , 9th Marine Regiment . Like his fallen colleagues , he amassed a host of honors in his military career , such as the Global War on Terrorism Expeditionary Medal and Sea Service Deployment Ribbon . • Cpl . Aaron J. Ripperda : At 26 , Ripperda was the most senior of those killed Tuesday , both in his age and rank . The Madison , Illinois , resident joined the Marine Corps in September 2008 , with his latest promotion to corporal coming in April 2011 . Among his numerous honors were a Navy Unit Commendation and a Humanitarian Service Medal . • Lance Cpl . Joshua C. Taylor : The Marietta , Ohio , resident , 21 , was a teenager when he joined the Marines in June 2010 . In 2011 , the decorated mortarman was promoted to lance corporal -- the same year he deployed to Afghanistan as part of Operation Enduring Freedom . • Lance Cpl . Mason J. Vanderwork : Another mortarman with a host of medals to his name , the 21-year-old Vanderwork was from Hickory , North Carolina . He , too , served in Afghanistan and accumulated a number of medals along the way . • Lance Cpl . William T. Wild IV : In October 2010 , the Anne Arundel , Maryland , resident joined the Marines . By December 2011 , the mortarman had earned his new rank -- and he also earned a number of recognitions , such as the Combat Action Ribbon and Global War on Terrorism Expeditionary Medal . He was 21 . Authorities still do n't know how the men died . McNulty said Wednesday they know only that the `` 60 mm mortar system failed to function as designed , '' and are trying to find out why . Hawthorne Army Depot , about 140 miles southeast of Reno , is used for storing ammunition and weapon stocks awaiting demilitarization . The facility also provides high-desert training facilities for military units . The night after the incident , the Marines issued a statement saying that 60 mm mortar rounds and tubes used to fire them are being pulled pending the investigation . In addition to the dead , eight servicemembers were injured in the explosion . The Wednesday night update from the Marines indicates that a Navy Corpsman remains `` very seriously injured , '' while five others are `` seriously injured '' and two Marines have been treated for minor injuries and released . CNN 's Barbara Starr , Mike Mount and Tina Burnside contributed to this report .
Those killed hail from different countries . One has been in the Marines since 2008 , another joined a few months ago . 8 were killed in the attack , all of them ` ` very seriously , '' the Marines said . Authorities still do n't understand why the mortar system ` ` failed to function as planned ''