WASHINGTON — The helicopter training crash earlier this week in the desert of Southern California killed three early-career Marines in their 20s and a 33-year-old crew chief who had served two tours in Iraq, Corps officials said Thursday.

The Marines’ CH-53E Super Stallion helicopter wrecked Tuesday as the crew practiced landing the heavy lift chopper on ungroomed grounds about 15 miles west of El Centro, California along the Mexican border, the Marines said in a statement.

All four Marines were assigned to Marine Heavy Helicopter Squadron 465 at Marine Corps Air Station Miramar north of San Diego. Their training mission had begun at the Marines’ Mojave Desert training post, Marine Corps Air Ground Combat Center Twentynine Palms, said Capt. Morgan Frazer, a service spokesman.

Killed were Capt. Samuel A. Schultz, 1st Lt. Samuel D. Phillips, Gunnery Sgt. Derik Holley and Lance Cpl. Taylor J. Conrad, Frazer said. The cause of the crash remains under investigation.

"The hardest part of being a Marine is the tragic loss of life of a fellow brother-in-arms,” said Col. Craig Leflore, the commander of Marine Aircraft Group 16, which oversees the fallen Marines’ unit. “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 -- its people.”

The oldest of the Marines killed in the crash, the 33-year-old Holley, had served in the Corps since 2003, according to the Marines. The crew chief from Dayton, Ohio was a veteran of several deployments, including two combat tours in Iraq and another to Japan with the 15th Marine Expeditionary Unit.

On a Facebook page for veterans of a unit in which Holley had once served, Marines wrote he left behind a wife and young son, recalling him as a solid Marine.

Holley was “a genuinely good dude who would talk to anybody and as best I can recall one squared-away Marine,” wrote one Marine who said he had served with him.

Schultz and Phillips were Marine pilots who were flying the aircraft, the military’s heaviest and most powerful helicopter.

Schultz, 28, of Huntington Valley, Penn., had served in the Corps since 2012, when he was commissioned through Penn State University’s ROTC program. He had served one deployment with the 11th Marine Expeditionary Unit, according to the Marines.

The captain’s father was also a pilot, his mother Julie Rosoff Schultz told the San Diego Union Tribune, saying “flying was in his blood.”

“He loved adventure,” she told the newspaper. “He sailed. He fished. He was a motorcycle rider. He jumped out of an airplane once. He enjoyed life and people loved to be around him.”

Phillips, 27, of Pinehurst, N.C., had joined the Corps in 2013. He had not deployed but had served previous assignments at Naval Air Station Pensacola in Florida, Naval Air Station Corpus Christi in Texas and Marine Corps Air Station New River in North Carolina, according to the Corps.

The youngest of the four fallen Marines, Conrad, 24, of Baton Rouge, La., had also not yet deployed, according to the Marines. He joined the Corps in 2016.

Conrad was a 2012 graduate of Central High School in Baton Rouge where he played football, ran track and competed in power lifting, the school’s head football coach Sid Edwards told The Associated Press.

The coach said Conrad had expressed interest in teaching special needs children after serving in the Marines. Edwards, whose own children both have autism, said Conrad had taken to working with them.

“Every one of those kids just absolutely adored him and would look forward to him being there,” Edwards told the AP. “It was like Elvis walking in a room … We’re talking about a very special, unique human being with a gift.”

The Marines were among five U.S. military aviators to die in a rash of training crashes in recent days. Maj. Stephen Del Bagno, a member of the Air Force’s elite demonstration squad the Thunderbirds, was killed Wednesday when his F-16 crashed near Nellis Air Force Base outside Las Vegas during preparations for an airshow this weekend.

In Africa, a Marine pilot suffered minor injuries after ejecting from his AV-8B Harrier attack jet upon takeoff from an airport in Djibouti on Tuesday. Another CH-53E was damaged in yet another incident Tuesday in Djibouti.

U.S. and Djiboutian officials have since agreed to temporarily ground all American military flights from the tiny nation on the Horn of Africa, said Marine Lt. Gen. Kenneth McKenzie, the director of the Joint Staff.

McKenzie said Thursday military officials were investigating each of the recent crashes, but the Pentagon had not determined whether there were correlations between the recent incidents. Other recent incidents included the fatal crash March 14 of a Navy F/A-18 Super Hornet off the coast of Key West, Fla., that left two pilots dead. An Air Force HH-60 Pave Hawk crash in western Iraq, also last month, killed seven airmen.

“Mishaps happen in military aviation any time you're flying complicated machines in situations where you've got less than total visibility and doing things that are difficult to do,” McKenzie told reporters Thursday at the Pentagon. “Mishaps are inevitably going to occur. We don't want any mishaps to occur. One mishap is too many. But I'm not prepared to say right now that this is some kind of crisis.”

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