Authorities just made the tragic announcement that the search for eight missing members of the United States’ military off the coast of California has been called off after forty hours, with all of them now presumed dead.

The New York Post reported that the seven Marines and one Navy sailor had been missing since Thursday, when an amphibious assault vehicle sank in hundreds of feet of water during a training exercise.

“It is with a heavy heart that I decided to conclude the search and rescue effort,” said Col. Christopher Bronzi, commanding officer of the 15th Marine Expeditionary Unit. “The steadfast dedication of the Marines, Sailors, and Coast Guardsmen to the persistent rescue effort was tremendous.”

“All eight missing service members are presumed deceased,” the unit wrote on Twitter on Sunday “Efforts will now turn to search and recovery.”

A total of sixteen members of the military were on the amphibious craft when it started taking on water in the middle of the exercise. Three of the service members were rescued from the craft and rushed to the hospital, where one passed away. The other two remain in critical condition at this time. Five others were rescued with no injuries and have since returned to their normal duties.

The names of the missing service members have not yet been released, and it is not yet known what caused the mishap in the first place. The Coast Guard, Marine Corps and US Navy spent forty hours searching 1,000 square nautical mile for the missing service members, but they have yet to turn up any trace of them.

Authorities believe the 26-ton military vehicle is lying hundreds of feet below the surface, which makes finding it an incredibly difficult task. At the time of the mishap, the vessel was returning to its base.

“They signaled to the rest of the unit that they were in fact taking on water,” Lt Gen Joseph Osterman said, according to The Guardian. “Immediate response was provided by two additional amphibious assault vehicles (AAVs) as well as a safety boat.”

“It sank completely,” he added, going on to say that it was in several hundred feet of water. At “26 tons, the assumption is that it went all the way to the bottom.”