‘One-in-a-million’ malfunction caused Marine artillery round to explode over highway, report finds
A fuze malfunction, the second in the model’s service history, likely caused an M795 155mm artillery shell to prematurely detonate during a live-fire demonstration at Camp Pendleton last fall, showering shrapnel on a civilian highway, the Marine Corps has found.
Marine Corps self-published internal investigation It’s about the incident that took place on Friday, October 18th. The incident last fall saw an artillery shell prematurely explode on Interstate 5 as Marines were conducting live-fire bombardment as part of an amphibious assault demonstration. The event, held as part of the Marine Corps’ 250th birthday celebration, was attended by Vice President J.D. Vance and Secretary of Defense Pete Hegseth, causing confusion in the hours before and prompting a last-minute closure of Interstate 5 near the base. Later in the celebration, electronic signs placed along the highway dozens of miles from the base warned drivers of “Live guns on the highway” as they approached Camp Pendleton.
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The Marine Corps determined that the projectile’s electronic fuze was malfunctioning, although the cause of the problem was unclear. According to the report prepared for the commander of I Marine Expeditionary Force, the fuze was “manufactured to a one-in-a-million defect standard.” Six M777 howitzers were deployed to Red Beach and crewed by Marines from 2nd Battalion, 11th Marine Regiment, 1st Marine Division. They were going to open artillery fire on the training area at Camp Pendleton on the other side of the highway. The Marine Corps said 120 artillery shells were available for the demonstration and that the shells were fired over Interstate 5, one of California’s busiest highways and serves as the main route between San Diego and Los Angeles; Camp Pendleton is located between the two cities. An Amtrak train line also runs parallel to the highway near the base.
Investigators were unable to determine what caused the malfunction but said the proximity of the howitzers to each other may have contributed to it. The six fired guns were packed close together, placed in an area of 165 yards by 165 yards, and the two howitzers were spaced only 14 feet apart. The report noted that “several career artillery officers stated that they had never seen howitzers placed so close together, but also acknowledged that there was no restrictive minimum distance for Gun placement in relation to administrative artillery live fire.” Additionally, the “presence of anomalous electromagnetic energy in the vicinity” of artillery guns may also have played a role, although the report does not detail what this means.
“The M767A1 fuze is extremely reliable and has only one failure in its service history,” the report said. This incident occurred at Fort Drum in 2017, when the same fuze mounted on a 105mm M119A3 round exploded prematurely after hitting something in flight.
Marines from 2nd Battalion, 11th Marine Regiment, 1st Marine Division reload an M777 lightweight 155mm howitzer during the 250th Amphibious Capability Demonstration rehearsal at Marine Corps Base Camp Pendleton, battle town of Red Beach, Oct. 17, 2025. Marine Corps photo by Gunnery Sgt. Aaron S. Patterson.
Experts, including engineers at the Corona Naval Surface Warfare Center in California, examined evidence of the events leading up to the incident. The projectile exploded 453 meters above the highway. Shrapnel, including a five-inch-long piece, fell to the ground and struck a California Highway Patrolman’s car and motorcycle. No one was injured. The two vehicles hit by falling shrapnel were assigned to Vance’s security detail; Vance was not nearby, instead on the stage where the event’s speakers were located.
The report also noted that President Donald Trump was prepared to participate in the amphibious landing demonstration, which would initially require the highway to be closed by Camp Pendleton. However, Vance, a former sailor, went in his place, creating the possibility that traffic would be allowed to pass.
The early explosion was the culmination of a chaotic period after the Marine Corps, following its own risk assessment, initially determined there was no need to shut down. The California government, after back-and-forth discussions with the military and federal government, decided to close the 27-mile highway near the base for several hours due to safety concerns. These included the direct risk of artillery and the potential risk that the sound of artillery could cause by startling or distracting drivers.
It was later revealed that the Marines had fired 30 155mm artillery rounds on Interstate 5 during a rehearsal the day before, while the freeway was still open and cars were passing under the ammunition arc. In the fall, the California Highway Patrol said the Marine Corps did not specify that the rehearsal would involve the firing of live artillery shells, but the Marine Corps claimed this was announced to California authorities.
