Marine Artillery Malfunction Sends Shrapnel onto California Interstate

A Marine Corps investigation reveals an extremely rare artillery shell malfunction during a live-fire demonstration caused debris to hit patrol vehicles on Interstate 5. The incident occurred during a military anniversary celebration attended by high-ranking officials at Camp Pendleton last October.

A Marine Corps investigation has determined that an extraordinarily rare equipment failure during a live artillery demonstration at Camp Pendleton caused metal fragments to shower Interstate 5, damaging two California Highway Patrol vehicles last October.

The incident happened during a military celebration marking the Marine Corps’ 250th anniversary, with Vice President JD Vance and Defense Secretary Pete Hegseth in attendance. Debris from the malfunctioning shell scattered across the closed interstate, hitting both a patrol car and motorcycle.

According to a comprehensive 666-page investigation report released December 19 and first disclosed Monday, military officials found “no definitive answer” for why the M795 high explosive round detonated prematurely at approximately 1,480 feet above ground. The report states such early detonation goes “beyond reasonable expectations and should not have happened, but it did.”

“It is manufactured to a tolerance of one defect in a million,” the investigation states. Officials determined no Marine personnel acted negligently or improperly.

Following the mishap, 26 California House representatives and both state senators wrote to Hegseth demanding answers about who authorized firing live rounds over the freeway and what safety measures were implemented.

The incident intensified tensions between President Donald Trump and California officials, including Governor Gavin Newsom. Some Republicans initially criticized Newsom for shutting down a 17-mile section of the highway before the exercise, while local leaders questioned the unconventional military display they believed was staged for 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 Newsom spokesperson, stated Tuesday.

Prior to the celebration, Newsom had criticized the highway closure, characterizing the live-fire exercise as an intimidation tactic against Trump critics who were holding “No Kings” demonstrations throughout San Diego that day.

“Firing live rounds over a busy highway isn’t just wrong — it’s dangerous,” Newsom stated at the time.

The Marine investigation identified multiple possible contributing factors to the malfunction, including howitzer cannons positioned too closely together during firing and the “potential presence of anomalous electromagnetic energy in the vicinity.”

The October 18 demonstration at Marine Corps Base Camp Pendleton showcased aircraft, naval vessels, and amphibious vehicles for the anniversary event. The planned artillery display involved 60 rounds fired across the coastal highway, according to an October CHP incident report.

“It will be a good show regardless of who shows up,” Gen. Eric Smith, Marine Corps commandant, wrote in an October 14 email to Brig. Gen. Garrett “Rainman” Hoffman from the White House Military Office.

Military and public safety officials noted the location was atypical. While live-fire training occurs regularly, it typically happens on designated ranges within the 195-square-mile base located north of San Diego.

The initial round fired at 1:46 p.m. from M777 howitzers positioned on a beach west of Interstate 5 failed to clear the roadway and exploded mid-flight near southbound I-5, sending fragments toward protective details assigned to the vice president. Officials immediately stopped the exercise and fired no additional munitions, CalMatters reported in October.

One officer reported hearing sounds like “pebbles” hitting his CHP BMW motorcycle, while other fragments struck an unoccupied Ford patrol vehicle. The two officers who had been using that vehicle discovered a 2-inch by ½-inch shrapnel piece on the hood, creating a small dent. Incident report photographs show the damaged patrol car and an officer holding the metal fragments.

In a December 5 statement included in the military report, an unnamed Marine said the Secret Service requested the I-5 closure for security reasons involving a “Very Very Important Person” — the president — due to proximity to the demonstration viewing area. Trump ultimately did not attend the event.