The U.S. Marine Corps investigation into last October’s live-fire demonstration over Interstate 5 concluded that a rare ammunition malfunction detonated early and sent shrapnel onto the highway, where it struck California Highway Patrol vehicles. The Marines said the incident occurred during a celebration of the Marine Corps’ 250th anniversary at Camp Pendleton and that investigators found no negligence or wrongdoing by Marines.
The Marines’ account centered on an Oct. 18 demonstration in which artillery was fired over the freeway, according to the report dated Dec. 19 and first reported this week. The investigation said an artillery shell exploded over the highway that serves as the main corridor between Los Angeles and San Diego, during an event attended by then–Vice President JD Vance and Defense Secretary Pete Hegseth, and that nobody was hurt.
In the report, Marine Corps investigators said the M795 high explosive round detonated prematurely at an altitude of about 1,480 feet (450 meters). The Marines said this kind of premature detonation was “beyond reasonable expectations and should not have happened, but it did,” and the report described the event as one “manufactured to a tolerance of one defect in a million,” the Associated Press reported.
The Corps also said there was “no definitive answer” for why the round detonated early. Investigators wrote that such a result was not what they expected based on prior use of the same shell-fuze combination and weapons system, and they pointed to multiple potential contributing factors, including howitzer guns being too close together when fired and the “potential presence of anomalous electromagnetic energy in the vicinity,” according to the report.
The Marines said organizers had planned to fire 60 rounds of live artillery in five minutes over the highway, using six howitzer weapons, but a round in the first volley failed and detonated early. The remainder of the demonstration was canceled, and the investigation tied the early detonation to shrapnel landing on the Interstate 5 roadway southbound.
The California Highway Patrol reported that the first round launched at 1:46 p.m. from M777 howitzers on a beach west of Interstate 5. The CHP said the artillery round detonated midflight near the freeway, sending shrapnel toward a CHP motorcycle and another unoccupied patrol vehicle that were near a ramp after escorting Vance, with sergeants conducting a safety sweep that found no other pieces of metal in the highway lanes. Both sides of the highway were reopened about 30 minutes later.
The Marines said multiple people interviewed for its investigation indicated they would not have changed anything about the event. Some interviewees said a drill the day before had not involved similar problems and that routine safety checks had been conducted, “more than usual,” the report said.
The episode also highlighted political conflict around whether the demonstration should have used live artillery over an active freeway. The day before the event, Gov. Gavin Newsom called the planned live-fire demonstration dangerous and unnecessary, ordered Interstate 5 closed during it, and later described the exercise as a show of force intended to intimidate political opponents who were demonstrating around San Diego under the “No Kings” protests banner.
Newsom’s decision drew condemnation from the White House and other Republicans, and the Marine Corps said the exercises would not endanger motorists. In an email Tuesday, Diana Crofts-Pelayo, a spokesperson for Newsom’s office, said the Marines’ investigation was “in stark contrast” to what she described as “dangerous and performative demands” by Vance and Hegseth to shoot live ammunition over a civilian area for entertainment.
The Marines’ report also recounted statements about the event leading up to the firing. It said Gen. Eric Smith, commandant of the Marine Corps, told Brig. Gen. Garrett “Rainman” Hoffman of the White House Military Office in an Oct. 14 email that “It will be a good show regardless of who shows up,” according to the investigation.
While the report did not provide a definitive explanation for the early detonation, it said the malfunction’s timing and nature were inconsistent with prior expectations and that investigators ruled out negligence or wrongdoing by Corps members, the Associated Press reported.