Marine Corps artillery mishap part of unusual firing over highway

By Haley Britzky, CNN

(CNN) — The US Marine Corps is no stranger to firing live ordnance as part of training, but it had been years — more than 70, according to one US official — since Marines had fired artillery over a stretch of the I-5 interstate in California like troops did last weekend during the Corps’ 250th birthday celebration.

The very first shell fired as part of the demonstration exploded on Saturday over the interstate, stretches of which serve as the busiest highway in America, dropping at least one shell fragment on a parked California Highway Patrol cruiser. The celebration at Camp Pendleton, California, was attended by Vice President JD Vance and Defense Secretary Pete Hegseth.

The Marine Corps is currently investigating what went wrong with the round, a 155mm artillery shell that had been fired by an M777 Howitzer.
The day before Marines had successfully fired more than two dozen shells from the same batch of artillery, according to the official, lending more questions as to what happened on Saturday and why.

CNN has reported there were no injuries from the incident, which the California Highway Patrol Border Division Chief Tony Coronado called “an unusual and concerning situation.”

The Marine Corps did not respond to questions about who made the decision to fire over I-5, when the last time was that the Marine Corps fired artillery over the interstate, or if there were broader concerns regarding the artillery batch the shell that prematurely detonated came from.

The US has been rapidly increasing its production of the 155 mm shells, more than tripling production since 2022 up to 40,000 rounds per month that has included opening new production facilities as part of $5.5 billion in US investment in manufacturing the munitions. The driver of that surge in production has been Ukraine’s need for the shells in its protracted war repelling Russian forces, with the US already having sent more than 3 million 155 mm rounds to the country since the start of the conflict.

California’s Gov. Gavin Newsom, in an escalating spat with the White House over the safety of Saturday’s demonstration, had closed the interstate ahead of the exercise, which involved firing artillery from a beach area over the highway onto land that is part of the Camp Pendleton military facility.

After Newsom had described plans to fire shells over the highway as “dangerous” and said he was making the decision to close the highway, a spokesman for Vance had told CNN that the showcase was “an established safe practice.”

Live-fire exercises, where real ordnance is used for training, are a common occurrence for US military units around the country. However, the specific route planned for the shells on Saturday hadn’t been used since before I-5 became an interstate in the 1950s, according to the US official.

“Firing from the beach, firing over I-5, in theory shouldn’t have been a problem,” Mark Cancian, a retired Marine Corps colonel who served as an artillery officer and who is currently a senior adviser at the Center for Strategic and International Studies, told CNN.

“The shells were high when they went over I-5 and that’s why the Marine Corps apparently said shutting down the highway was not necessary because in theory, they’d be so high they wouldn’t interfere with anyone below,” he said. “And for some reason one of them went off prematurely.”

The batch of artillery shells used during the demonstration has likely been frozen and will not be used again until the Marines further clarify what happened, Cancian said.

A 2024 Reuters investigation of artillery production found some issues with manufacturing lines of the munitions, including cracked shells in Iowa that shut down a production line further delaying their delivery, and a US decision to change the kind of explosive used in the shell.

Years before Russia’s invasion of Ukraine, the US decided to move away from using TNT inside the shell to an explosive believed to be “less vulnerable to detonation by accident,” the Reuters report said.

The Army confirmed to Reuters it reversed course and began using TNT once again after the war began, due to cost efficiency needs and to increase the production rate.

The military services often try to put together a compelling showcase when important leaders make a visit to a military facility, Cancian said.

“The idea that when a VIP shows up you do something special for them is totally normal,” he said.

What is abnormal, he added, is that the shell detonated prematurely. The 155 shells, Cancian explained, weigh roughly 95 pounds – the majority of that weight due to the shell itself, and only 15 pounds of it attributed to the actual explosive. When the shell explodes, the metal casing is meant to splinter into tiny fragments in an effort to inflict more casualties on a battlefield.

A photo of one of those fragments on a patrol car was shared in a press release by the California Highway Patrol, which said shrapnel struck and damaged a patrol vehicle. Cancian emphasized that the patrol car was not “hit” by an artillery shell but rather struck by fragments of the shell which exploded far overhead, slowing down as they fell through the air before landing on the patrol car.

“It went off very high, and the shell fragments came down to the ground, didn’t look like they were going very fast,” he said, adding that “obviously that should not have happened.”

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