Sometime before April 16, 2013, one or more people scouted the Pacific Gas and Electric Company’s high-voltage Metcalf substation off Highway 101 near San Jose, California. They went around the unmanned power station at a range of 40-60 yards, marking places from which the transformers’ cooling fins were clearly visible through the chain-link fence with piles of stones.

According to a Wall Street Journal report last week, at about 1 a.m. on that April 16, someone cut the telephone lines going to the substation’s location in a manner calculated to be hard to repair. Within about another thirty minutes, shooters took positions by the stone piles and — on a flashlight signal — opened fire. The firing — over about a twenty-minute period, apparently using AK-47 rifles (identified by the empty shell casings in 7.62×39 caliber left behind) — aimed 120 shots at the cooling fins on the transformers, scoring 110 hits. Another flashlight signal called a cease-fire. The shooters were gone long before the first police arrived.

A bullet is a pretty low-tech device, but in this case they were highly effective. Seventeen huge transformers were knocked out. Those 110 holes leaked about 52,000 gallons of coolant and were about to cause power failures in the Silicon Valley grid but managers were able to switch power in from other locations. They were lucky: the hour of the attack and the season meant there was low demand for electric power.

Police and FBI found those 120 empty cartridge casings. They were wiped clean of fingerprints and yielded no DNA for testing.

The fact that the telephone lines were located and the rock piles placed at the best firing points indicates a pretty thorough reconnaissance of the target by people more skilled than your average barflies. It would take a fair amount of knowledge of the high-voltage system to target the cooling fins rather than the transformers themselves and to choose a weapon that could destroy the cooling fins but would not likely puncture the transformers which would have caused an explosion.

The facts that the firing began and ended with a flashlight signal, that 110 of 120 shots hit the targets, that the shell casings were wiped clean, and that the perpetrators vanished long before the police arrived indicates a fairly high level of discipline, training, and skill.

In short, this was a terrorist attack. It’s important to determine whether it was perpetrated by home-grown terrorists or by terrorists infiltrated from overseas. If overseas terrorist groups mounted this sort of attack, it would be more likely to prove to be a rehearsal of a larger attack to come later. Domestic terrorists don’t operate on that large a scale, at least so far.

There have been no arrests in the case. The FBI says that the attack wasn’t the work of terrorists. Jon Wellinghoff, who was chairman of the Federal Energy Regulatory Commission at the time of the attack, disagrees.

Wellinghoff is obviously correct. He has been quoted in several reports on the attack. I spoke to him on Saturday to get his views account directly.

Soon after the attack Wellinghoff traveled to the power station accompanied by Defense Department experts who were part of a group that, he said, trains special operations troops how to attack infrastructure targets. They inspected the site, seeing the damage, the rock piles and concluded that it was a “targeting package” designed to cripple the power station by people who knew what they were doing.

Mr. Wellinghoff was pretty direct. He said, “There was a purposeful, well-planned and well-executed attack on a very large piece of our national grid infrastructure.” He attributes a high degree of knowledge and training to the attackers because they hit the cooling fins rather than the transformers or the bushings, either of which could have caused a quicker power failure — or even an explosion — which might have left less time for the attackers to escape.

Wellinghoff states his disagreement with the FBI strongly. They won’t say that it was a terrorist attack, but he says it definitely was. “I’ve had multiple contacts with the FBI including briefing the current director of the FBI personally on this event. My understanding from the FBI is that they have no evidence to determine that this is linked to a known terrorist group. That is their position. But they also have no evidence at all to do anything. The only evidence they have is 120 brass [empty cartridge cases] that have no fingerprints and no DNA. So they have no evidence of anything.”

There the FBI position is a big quibble. If there’s no evidence to link the attack to a “known terrorist group,” that’s no reason to rule out terrorism altogether. Evidence, gathered later, could lead in any direction.

Organization, training, and skill aren’t concealable. It is hard to get away from the fact that these terrorists knew more than the general public about what parts of the power substation should be hit to cause the most damage and at the same time give them the least likelihood of being caught in the act. 

It’s certainly possible that a very small group is involved. I can see how a group as small as three people could perpetrate the attack. Two or three people had to enter the telephone vault (through a door/hatch reportedly too heavy for one man to handle) and cut the lines in a particularly hard to repair way. Then one scout could keep watch for police and to signal and two shooters rotating quickly between firing positions. The shooters could easily put 110 of 120 shots on target in the twenty minutes or so the firing took. But it’s useless to speculate whether that small a group was solely responsible or whether they are a part of a larger group.

What is important is that, as Mr. Wellinghoff said, we have proof of the vulnerability of these targets. If the Metcalf substation had been hit at a time of high demand, there could have been a big blackout in Silicon Valley. If the attack had been timed so that several substations were attacked within hours or days, a large section of the nation could have been blacked out perhaps for weeks.

According to Wellinghoff, there are about one hundred of these power substations around the country that are really critical to the grid. They need to be protected, which will cost money. They are unguarded and guarding them is not the entire answer. Even the best guards aren’t going to be able to protect a thousand-yard perimeter around each substation.

The cheaper answer is, as Wellinghoff prescribes, making the fences around the substations higher and opaque so that shooters would have a tougher time. Jersey wall barriers — ten feet high or more — could be added. Neither would be sniper-proof where hills or tall buildings provide better vantage points, but they would help.

It’s fashionable to worry about cyber terrorists knocking out power plants but when our power grid is so evidently vulnerable to attack with low-tech weapons, we need to take action to protect from both sorts of terrorism. Financial help from the government will not to be forthcoming. The government is still unable to help because it’s spending money on such urgent priorities as Victoria Nuland’s salary and subsidies for purchasing her automotive equivalent, the Chevy Volt.

The power companies need to take protective measures themselves. Once the federal government gets into the act, and it will, the protective measures will only get more costly without any guarantee of being more effective.