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CAMP PENDLETON, Calif. – An investigation is underway Thursday at Camp Pendleton, where an amphibious landing vehicle caught fire during a training exercise, injuring 15 Marines, five critically.

The accident occurred about 9:30 a.m. Wednesday as the Marines were undergoing regularly scheduled land-based training in the northern reaches of the sprawling base near Oceanside, said 1st Lt. Paul Gainey, a spokesman for the Marine Corps’ 1st Marine Division.

Eight of the injured Marines were taken to UCSD Medical Center, where three were admitted in critical condition and five in serious condition.

Four others were transported to UC Irvine Medical Center in the city of Orange in Orange County, where two were listed as critical and two were in unknown condition. Another Marine was admitted to Scripps Memorial Hospital La Jolla in stable status, and two were treated at Naval Hospital Camp Pendleton for minor injuries.

“The 1st Marine Division would like to thank the civilian and military emergency personnel who responded immediately to the situation and allowed the injured Marines to receive rapid care,” Gainey said. “Our thoughts and prayers are with the Marines and their families affected by this incident.”

The type of vehicle that caught fire, an amphibious assault vehicle commonly called an Amtrack, has been used since the 1970s to transport Marines from sea to land.

In September 2013, 21-year-old Marine Cpl. Nicholas Sell was killed and four others were injured in a training accident when their Amtrack caught fire at Marine Corps Air Ground Combat Center Twentynine Palms in the Mojave Desert.

Officials determined ordnance from a mine-clearing system was to blame for the fire and stopped using that mine-clearing system until releasing a safer version earlier this year, according to

“While certainly the last four years have been spent making the (MK-154 Mod 1) system more reliable and driving down the cost of maintenance, the big driver for the past four years was to ensure that we put out a system that was vastly safer,” said Robert Davies, a safety official with Marine Corps Systems Command, in a statement to the website.

Photos and videos provided by the Marine Corps showed the new system being tested on an Amtrack at Camp Pendleton. It was not immediately known if the updated new mine-clearing system was responsible for sparking the Amtrack fire Wednesday.