Mark J. Terrill, AP
In light of the newly reported details of the San Jose power substation attack, we can no longer take for granted the physical security of our electrical grid.

Last week, thanks to top notch investigative reporting by the Wall Street Journal, the general public learned of an armed attack on a power substation on the outskirts of San Jose. The attack occurred last April, and knocked out 17 large transformers that supply electricity to Silicon Valley. While fast acting power company personnel were able to reroute power into San Jose, avoiding blackouts, the damage to the facility was so extensive that it took nearly four weeks to repair. While PG&E, the power company that owns the substation, reported that the incident was an act of “vandalism”, it just might be the most significant terrorist attack on US soil in years. It certainly exposed the precarious security situation of our national power grid. Here is what happened.

Last year, about 1 a.m. on Tuesday morning April 16, unknown assailants broke into an underground utility vault near the PG&E San Jose power substation, and cut the fiber-optic telecommunications cables serving the area. Thirty minutes later, taking up firing positions that appear to have been pre-scouted and marked, the assailants opened fire on the massive power transformers with AK-47 style weapons, calmly targeting one substation at a time.

About 10 minutes into the attack, motion sensors at the substation, most likely triggered by bullets grazing the chain link fence surrounding the facility, alerted PG&E of a disturbance, and minutes later an engineer at a nearby power plant called police to report gunfire. It took police another 10 minutes to make it to the scene, but mere moments before they arrived, the assailants stopped shooting, dissolved into the hills and disappeared. Without access to the locked power substation and without the equipment or resources to pursue the shooters, the police left the scene. The next morning, investigators found over 100 shell casings of the sort ejected by AK-47s, not one of them with a trace of a fingerprint.

By all measures, the attack on the San Jose power substation was a professional job. The assailants knew exactly what they were doing, and acted with military precision. Even now, nearly 10 months later, investigators have made no progress in finding the perpetrators. We don’t know who these people are and can only speculate as to their motives.

But one thing is disturbingly clear – our power grid is at risk. There are only around 2,000 very large transformers supporting the United States’ three electrical networks. These transformers can weigh upwards of 500,000 pounds and take weeks, even months, to replace when damaged. A coordinated attack, like the one outside of San Jose, on a relatively small number of power substations could shut down our electrical grid, sever the flow of news and information, and plunge the country into darkness for weeks.

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Over the past three years, we have heard several times that our national power grid is vulnerable, with significant media attention focused on the ongoing cyber attacks that continuously probe the grid for weaknesses. But there have also been 274 direct, significant acts of “vandalism” to power substations over the last three years that have received very little attention. In light of the newly reported details of the San Jose power substation attack, we can no longer take for granted the physical security of our electrical grid.

Just as the federal government is working to protect our electrical grid from cyber attacks, so too should it help utility companies defend key electrical substations from physical attacks. It is not sufficient to simply replace chain link fences with opaque ones, as PG&E is planning to do. With so much at stake, much more is required.

Dan Liljenquist is a former state senator and former U.S. Senate candidate.