(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.
"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 don'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.