CAMP PENDLETON, Calif. » A Marine died after going down with an amphibious assault vehicle that sank Friday during a training exercise in a harbor in Southern California, authorities said.

The man was pulled from the vehicle at about 2:15 p.m. and flown to Scripps Memorial Hospital in La Jolla, where he was pronounced dead, the Marine Corps at Camp Pendleton said. His name was being withheld until relatives were notified.

Five other Marines escaped without injury from the training vehicle as it became submerged shortly before noon in the Del Mar boat basin in San Diego County’s Oceanside Harbor, the Corps said.

Three instructors and three students from the Assault Amphibian School Battalion were conducting initial driver training when the vehicle sank, Maj. Daniel Thomas, the executive officer or second in command of the battalion, told the San Diego Union-Tribune. It wasn’t immediately known whether the dead man was an instructor or a student.

They were operating about 300 feet offshore in water 30 to 40 feet deep while a companion vehicle waited nearby, he said.

"We are not placing a hold on training. But obviously we are going to take a look at this and then the commander will make a decision before anything goes back into place, to make sure any safety briefings that need to be given are conducted," Thomas told the Union-Tribune.

The Marine Corps said the incident was under investigation and it was not known what caused the vehicle to sink.

The vehicle is a type of seafaring tank armed with a .50-caliber machine gun and a grenade launcher that is used to transport Marines to shore, according to the Union-Tribune.

When driven off a ship, the 32-ton armored vehicles often drop below the surface before they pop above water. They travel at about 8 miles per hour on water and 45 miles per hour on land, and can carry as many as 24 fully loaded combat Marines into battle.