One US marine has died and eight others are missing after an amphibious assault vehicle (AAV) accident off the coast of southern California.
Two personnel were also injured in the accident on Thursday, the 1st Marine Expeditionary Force tweeted.
A search is under way for the missing service members, with Navy and Coast Guard help.
All the personnel are assigned to the 15th Marine Expeditionary Unit, based at Camp Pendleton, near San Diego.
Col Christopher Bronzi, commanding officer of the 15th MEU, said in the tweet: "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."
The 15th MEU has about 2,200 personnel and conducts rapid-response, conventional amphibious and other maritime operations.
The typical US Marine Corps AAV is the AAV-P7/A1, functioning as a troop carrier, transporting personnel from water to land. It is often referred to as an "Amtrac".