Those killed in the crash include Capt. Samuel A. Schultz; 1st Lt. Samuel D. Philips; Gunnery Sgt. Richard D. Holley; and Lance Cpl. Taylor J. Conrad, Marine Corps officials said in a release. All belonged to HMH-465, out of Marine Corps Air Station Miramar, California.
"The loss of our Marines weighs heavy on our hearts," Maj. Gen. Mark Wise, commanding general of 3rd Marine Aircraft Wing, said in a statement. "Our priority is to provide support for our families and HMH-465 during this critical time."
According to information provided by the Marine Corps, the fallen troops had a range of military and combat experience.
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Schultz, 28, of Huntington Valley, Pennsylvania, was a pilot who joined the Corps in May 2012, according to a release. He previously served at MCAS New River, North Carolina, and had deployed with the 11th Marine Expeditionary Unit.
Philips, 27, of Pinehurst, North Carolina, was also a pilot who had previously served at New River. He joined the Marine Corps in August 2013.
Holley, 33, of Dayton Ohio, was a combat veteran. A CH-53 crew chief, he joined the Marines in November 2003 and had twice deployed to Iraq in support of Operation Iraqi Freedom. He had also deployed to Japan as part of the United Deployment Program, and completed another deployment with the 15th MEU, according to the release.
His awards include the Navy and Marine Corps Commendation Medal, Navy and Marine Corps Achievement Medal (4th award), and Air Medal-Strike/Flight (9th award).
Conrad, 24, of Baton Rouge, Louisiana, was also a CH-53 crew chief. He joined the Corps in May 2016.
It's not clear what caused the helicopter to crash. The Associated Press reported the aircraft had been conducting routine desert landing training at the time of the mishap, about 15 miles west of El Centro.
The crash, the first of three major military aircraft mishaps in two days, two of them deadly, is still under investigation.
"The hardest part of being a Marine is the tragic loss of life of a fellow brother-in-arms," Col. Craig Leflore, commanding officer of Marine Aircraft Group 16, said in a statement. " ... These 'Warhorse' Marines brought joy and laughter to so many around them. They each served honorably, wore the uniform proudly and were a perfect example of what makes our Marine Corps great."