Three US Marines who died when their Osprey aircraft crashed during a military exercise in Australia have been identified by their unit.

Corporal Spencer R. Collart, 21, Captain Eleanor V. LeBeau, 29, and Major Tobin J. Lewis, 37, were among 23 Marines on board the MV-22B Osprey when it crashed on Melville Island around 9:30 a.m. local time Sunday.

Collart was the Osprey crew chief, LeBeau a pilot and Lewis the executive officer of Marine Medium Tiltrotor Squadron 363 (VMM-363), their unit said Monday.

"We are deeply saddened by the loss of three respected and beloved members of the MRF-D (Marine Rotational Force-Darwin) family," said Col Brendan Sullivan, their commanding officer of the unit. "Our thoughts and prayers remain with the families and with all involved."

Of the other 20 Marines, three are still being treated in Royal Darwin Hospital. One of them is in critical condition, the other two are stable. The remaining 17 were treated for minor injuries and released.

The cause of the crash is under investigation.

US Defense Secretary Lloyd Austin offered his condolences to the families of those killed and injured.

"These Marines served our country with courage and pride, and my thoughts and prayers are with their families today, with the other troops who were injured in the crash, and with the entire USMC family," he said on X, formerly known as Twitter.

The aircraft that crashed was one of two US Marine Osprey aircraft that left Darwin Sunday morning and flew towards the Tiwi Islands, about 80 kilometers away, Australia's Northern Territory Police Commissioner Michael Murphy said.

Sullivan thanked the Australian forces and other groups who helped the Marines following the incident.

"We would like to express our sincere gratitude to the Australian Defence Force, Northern Territory Police, Northern Territory Government, CareFlight Air and Mobile Services, NT Health, National Critical Care and Trauma Response Centre, and Tiwi Island Government, who have come together to assist us in this difficult time," Sullivan said.

The crash comes just a month after four Australian army aircrew members died after an MRH-90 Taipan helicopter crashed into the sea near Hamilton Island off the east coast of Australia during an exercise that was part of joint drills with the United States.

It is the latest deadly crash to involve an Osprey aircraft. Generally, Osprey are safe to fly, but the aircraft has had a history of mechanical and operational issues since its inception in the 1980's, CNN military analyst and retired US Air Force Col. Cedric Leighton told "CNN This Morning."

A history of crashes

Previous crashes of Osprey aircraft, according to CNN reporting and US Defense Department news releases:

July 20, 1992: Seven people are killed during testing when an Osprey crashes in Virginia.

April 8, 2000: A crash during training in Arizona kills 19 Marines. The crash is blamed on pilot error, with investigators concluding the pilot tried to land too fast and at too steep an angle, causing a loss of lift.

December 11, 2000: Four Marines are killed when an Osprey crashes in North Carolina. The accident is later blamed on problems with a hydraulic part and a software anomaly in the aircraft's computer system.

April 8, 2010: US Air Force Osprey crashes in southern Afghanistan, killing three US service members and one civilian employee.

April 11, 2012: Two US personnel are killed in an Osprey crash in Morocco.

June 13, 2012: An Air Force CV-22 Osprey crashes during a routine training mission north of Navarre, Florida, injuring five.

May 17, 2015: A Marine Corps MV-22 Osprey crashes at Bellows training ground on Oahu, Hawaii, leaving two Marines dead.

December 13, 2016: An MV-22B Osprey lands in shallow waters off Okinawa, Japan, injuring two.

August 5, 2017: An MV-22B Osprey crashes off the coast of Australia, leaving three Marines dead.

September 28, 2017: A Marine Corps MV-22 Osprey crashes in Syria, injuring two service members.

March 18, 2022: Four US service members are killed when the MV-22 Osprey they are traveling in crashes during NATO training exercises in Norway.

June 8, 2022: Five US Marines die after an MV-22 Osprey crashes during a training mission Wednesday near Glamis, California.