Military report says 'one in a million' live fire malfunction rained shrapnel on California highway

LOS ANGELES (AP) — A “one in a million” malfunction during a 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 during a celebration of the 250th anniversary of the Marine Corps, attended by Vice President JD Vance and Defense Secretary Pete Hegseth. Pieces of shrapnel scattered on the closed roadway and struck a CHP patrol car and a motorcycle.

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). 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. Investigators ruled out any negligence or wrongdoing by Corps members.

Days after the malfunction, 26 California U.S. House members and the state’s two senators to Hegseth asking who decided to shoot live artillery over the freeway and how authorities prepared for the safety risks.

The mishap deepened conflicts between President Donald Trump and California leaders including , with some Republicans initially chastising the governor for closing a 17-mile (27-kilometer) stretch of the freeway ahead of the live fire exercise. Other local leaders were exasperated by an unorthodox military display that they believe was orchestrated for the benefit of Trump administration officials.

“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 ahead of the celebration, describing the live fire exercise as a show of force meant to intimidate Trump’s opponents, thousands of whom were demonstrating at throughout 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.”

The Oct. 18 demonstration at Marine Corps Base Camp Pendleton featured aircraft, ships, and amphibious assault vehicles to celebrate the anniversary. It involved firing artillery across the coastal freeway in a planned demonstration of 60 rounds, according to an October CHP incident report.

That location was unusual, military and public safety officials said at the time. Although live fire training is routine, it usually takes place on designated ranges within the 195-square-mile (505-square-kilometer) base north of San Diego.

The first round launched at 1:46 p.m. from M777 howitzers on a beach west of Interstate 5 toward the east, the CHP report stated. That artillery round failed to clear the roadway and detonated midflight near I-5 southbound, sending shrapnel flying toward protective service details assigned to the vice president. After that, the exercise was halted and no more munitions were fired.

An officer described hearing what sounded like “pebbles” falling on his CHP BMW motorcycle, and other shards struck an empty Ford patrol vehicle. The two officers who had driven the vehicle saw a 2 inch by ½-inch piece of shrapnel on the hood, which left a small dent or scratch. Photos in the incident reports show the patrol car struck by shrapnel, and an officer holding the metal shards.

In a Dec. 5 statement cited in the military report, a Marine whose name was redacted said the Secret Service wanted to close I-5 due to security concerns for a “Very Very Important Person” — the president — and its proximity to a viewing area for the demonstration. Trump ended up not attending.

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Associated Press reporters Ed White in Detroit and Rebecca Boone in Boise, Idaho, contributed to this report.