The U.S. Marine Corps on Friday identified five people who died when their Osprey tiltrotor aircraft crashed during training in the California desert.

Killed were two pilots: Capt. Nicholas P. Losapio, 31, of Rockingham, New Hampshire and Capt. John J. Sax, 33, of Placer, California.

Also killed were three tiltrotor crew chiefs: Cpl. Nathan E. Carlson, 21, of Winnebago, Illinois; Cpl. Seth D. Rasmuson, 21, of Johnson, Wyoming and Lance Cpl. Evan A. Strickland, 19, of Valencia, New Mexico.

The longest-serving Marine was Losapio, with 8 years and 9 months, while Strickland had been in the service for 1 year and 7 months

The MV-22 Osprey went down Wednesday afternoon during training in a remote area in Imperial County near the community of Glamis, about 115 miles (185 kilometers) east of San Diego and about 50 miles (80 kilometers) from Yuma, Arizona.

The Marines were based at Camp Pendleton and assigned to Marine Medium Tiltrotor Squadron 364 of Marine Aircraft Group 39, part of the 3rd Marine Aircraft Wing headquartered at Marine Corps Air Station Miramar in San Diego.

“It is with heavy hearts that we mourn the loss of five Marines from the Purple Fox family” the squadron’s commanding officer, Lt. Col. John C. Miller, said in a statement. “Our primary mission now is taking care of the family members of our fallen Marines and we respectfully request privacy for their families as they navigate this difficult time.”

The cause of the crash is under investigation.

The Marines were participating in routine live-fire training over their gunnery range in the Imperial Valley desert, said Marine Maj. Mason Englehart, spokesperson for the 3rd Marine Aircraft Wing.

The Osprey, a hybrid airplane and helicopter, flew in the wars in Iraq and Afghanistan but has been criticized by some as unsafe. It is designed to take off like a helicopter, rotate its propellers to a horizontal position and cruise like an airplane.

Versions of the aircraft are flown by the Marine Corps, Navy and Air Force.

Prior to Wednesday’s crash, Osprey crashes had caused 46 deaths, the Los Angeles Times reported.

Most recently, four Marines were killed when a Marine Corps Osprey crashed on March 18 near a Norwegian town in the Arctic Circle while participating in a NATO exercise.