A routine training exercise turned deadly for a Marine Expeditionary Force (MEF) unit on Thursday afternoon. One Marine is dead and others are missing in an AAV (amphibious assault vehicle) mishap off San Clemente Island in southern California.

“1 Marine has died, 8 service members remain missing and 2 were injured after an AAV mishap July 30 off the coast of Southern California,” the MEF tweeted early on Friday.

“All are assigned to the 15th MEU [Marine Expeditionary Unit]. Search and rescue efforts are still underway with support from the Navy and Coast Guard.”

The Marines, assigned to the San Diego-based 15th MEU, had been conducting a routine training exercise in coordination with the three-ship Makin Island Amphibious Ready Group and other assets assigned to the MEU. Around 5:45 p.m., the AAV reported taking on water, according to a news release from the MEF.

There were a total of 16 troops onboard the AAV: 15 Marines and one sailor. Of those, eight were able to make it out of the vehicle. One was evacuated to Scripps Memorial Hospital La Jolla outside of San Diego, where he was pronounced dead. Two more Marines were sent to local hospitals, where they remain. One of them is reported to be in critical condition and the other is stable, according to local reports.

The Navy and Coast Guard have initiated an extensive search and rescue operation. Four helicopters (three from the U.S. Navy and one from the U.S. Coast Guard), the USS John Finn, several small boats from the USS Makin Island, USS Somerset, and USS San Diego, as well as the Coast Guard cutter Forrest Rednour are participating in the operation.

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The one Marine who is reported dead in the accident has not yet been identified, as Pentagon rules specify a 24-hour notification period for the next of kin. 

“We are deeply saddened by this tragic incident. I ask that you keep our Marines, Sailors, and their families in your prayers as we continue our search,” Colonel Christopher Bronzi, 15th MEU Commanding Officer, said.

Amphibious Assault Vehicles ( AAVP-7A1) are tracked armored transport for Marines that can move on land or water. They are used by U.S. Marine Corps Assault Amphibious Battalions to land the surface assault elements from assault ships during amphibious operations. Marines often refer to them as “amtracs.”

AAVs have been in service with the Marine Corps since 1972 and are currently due to be replaced. In June 2018, the Marine Corps announced that it had selected the new Amphibious Combat Vehicle (ACV) program to supplement and ultimately replace the AAV.