A “one in a million” malfunction during a live fire demonstration over Camp Pendleton last October led to a misfire that rained shrapnel on Interstate 5, striking two California Highway Patrol vehicles, a U.S. Marine Corps investigation found.
An artillery shell exploded over the highway that serves as the main corridor between Los Angeles and San Diego during a celebration of the 250th anniversary of the Marine Corps, attended by Vice President JD Vance and Defense Secretary Pete Hegseth. Nobody was hurt, and investigators ruled out any negligence or wrongdoing by Corps members.
The day before the event, Democratic Gov. Gavin Newsom called the planned demonstration with live artillery dangerous and unnecessary, and he ordered I-5 to be closed during it. That closure drew condemnation from the White House and other Republicans, and the Marine Corps said the exercises wouldn’t endanger motorists.
In a 666-page report dated Dec. 19 and first reported on Monday, the Marines concluded that there “is no definitive answer” to why an M795 high explosive round detonated early at an altitude of about 1,480 feet (450 meters) during the Oct. 18 demonstration. Such a premature detonation is “beyond reasonable expectations and should not have happened, but it did,” the report says.
“It is manufactured to a tolerance of one defect in a million,” according to the report.
Organizers planned to fire 60 rounds of live artillery in 5 minutes over the highway, using six howitzer weapons, according to the report. But a round in the first volley of shots failed and detonated early, and the rest of the demonstration was canceled, the report said.
Days after the malfunction, 26 California U.S. House members and the state’s two senators sent a letter to Hegseth asking who decided to shoot live artillery over the freeway and how authorities prepared for the safety risks.
“We’re thankful to the Marines for their thorough and precise investigation — in stark contrast to the dangerous and performative demands by JD Vance and Pete Hegseth to shoot live ammunition over a civilian area for their entertainment,” Diana Crofts-Pelayo, a spokesperson for Newsom’s office, said in an email Tuesday.
Newsom announced the highway closure in a statement after practice rounds were fired a day ahead of the celebration. The governor described the live fire exercise as a show of force meant to intimidate Trump’s opponents, thousands of whom were demonstrating at “No Kings” protests in and around San Diego that day.
“Firing live rounds over a busy highway isn’t just wrong — it’s dangerous,” Newsom wrote at the time.
The Marine report concluded several factors could have contributed to the malfunction, including the howitzer guns being too close together when fired and the “potential presence of anomalous electromagnetic energy in the vicinity.”
“What was different from the thousands of times before this event employing the same shell-fuze combination, weapons system, and highly trained Marines? There is no definitive answer,” the report said.
The event at Marine Corps Base Camp Pendleton featured aircraft, ships, and amphibious assault vehicles to celebrate the anniversary.
“It will be a good show regardless of who shows up,” Gen. Eric Smith, commandant of the Marine Corps, said in an Oct. 14 email to Brig. Gen. Garrett “Rainman” Hoffman, of the White House Military Office, according to the investigation.
The first round launched at 1:46 p.m. from M777 howitzers on a beach west of Interstate 5. That artillery round detonated midflight near I-5 southbound, sending shrapnel flying toward a CHP motorcycle and another unoccupied patrol vehicle, according to the CHP report. The vehicles had been part of Vance’s protective service detail and were waiting near a highway ramp after securely getting Vance where he needed to be, the report said.
An officer described hearing what sounded like “pebbles” falling on his motorcycle, and finding shards nearby. Other shrapnel struck and left a dent on the hood of another patrol vehicle.
CHP sergeants conducted a safety sweep and didn’t find any other pieces of metal in the highway lanes, the report said. Both sides of the highway were reopened about 30 minutes later.
Multiple people interviewed for the Marines investigation said they wouldn’t have changed anything about the event. Some noted a drill the day before did not have any problems and routine safety checks were done more than usual.
