One Marine has died, two injured and eight others were missing after an amphibious assault vehicle accident off the coast of southern California, the Marines said early July 31.

The accident happened July 30 and search and rescue efforts were underway early July 31 with support from the Navy and Coast Guard, the Marines said in a tweet. All of the Marines involved were assigned to the 15th Marine Expeditionary Unit.

“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,” Col. Christopher Bronzi, the unit’s commanding officer, said in another tweet from the Marines.

The Marine Expeditionary Force is the Marine Corps’ main warfighting organization. There are three such groups which are made up of ground, air and logistics forces.

According to officials, the mishap happened at approximately 5:45 p.m., July 30 during a routine activity near San Clemente Island, when the vehicle began taking on water.

Also known as an AAV, the vehicle is meant to carry troops from ship to shore, particularly through rough water. San Clemente Island, part of Naval Base Coronado, is located about 80 miles northwest of San Diego.

One Marine with the 15th unit was pronounced dead at a hospital in La Jolla, Calif., on July 30, and two other Marines, one of them in critical condition, were transported to local hospitals.