The U.S. military announced Wednesday the grounding of all its Osprey CV-22 aircraft, one week after eight Air Force Special Operations Command service members died in a crash off the coast of Japan.

Lt. Gen. Tony Bauernfeind, head of Air Force Special Operations Command, directed the grounding "to mitigate risk while the investigation continues," the command said in a statement.

The military said that the "standdown" of the Osprey CV-22 aircraft will "provide time and space" for a thorough investigation and to ensure a safe return to operations.

The extraordinary decision to ground the entire fleet of Ospreys came after a preliminary investigation revealed that a material failure was the cause of the devastating crash — not a mistake by the crew.

US MILITARY IDENTIFIES ALL 8 CREW MEMBERS OF DEADLY AIR FORCE OSPREY CRASH NEAR JAPAN

A photo of an Osprey

A U.S. military CV-22 Osprey takes off from Iwakuni base, Yamaguchi prefecture, in western Japan. An Air Force Osprey crashed last week off southwestern Japan, killing its crew members.  (Kyodo News via AP/File)

A boat with lights at night

A Japanese coast guard vessel conducts a search and rescue operation around the site where a U.S. military Osprey aircraft was believed to crash in the sea off Yakushima Island, Kagoshima prefecture, southern Japan, on Nov. 29, 2023. (Kyodo News via AP)

In a release, the Air Force Special Operations Command said that the underlying cause of the failure was still unknown at that time.

JAPANESE, US MILITARY DIVERS DISCOVER WRECKAGE, REMAINS IN SEARCH FOR OSPREY AIRCRAFT THAT CRASHED OFF JAPAN

The military did not immediately say when the fleet would be back in commission

Eight service members died during the devastating crash off the shore of Yakushima Island, Japan on Nov. 29.

On Tuesday, military officials identified the service members who were on board the Air Force CV-22 Osprey.

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"Our thoughts and prayers are with the families, friends and peers of all who are impacted by this mishap and loss of life," said Bauernfeind. "In times like these, where service to our nation is not just a personal commitment but also a legacy woven into the fabric of our families, the depth of sorrow is immeasurable. 

"The honorable service of these eight Airmen to this great Nation will never be forgotten, as they are now among the giants who shape our history."