FBI investigates military style attack on California power station

As many as two attackers cut all phone service - both landline and cellular - to PG&E's Metcalf substation

Over 100 rounds of ammunition were fired at several transformers

Several were damaged, others shut down after leaking coolant caused them to overheat

The FBI initially believed the attack may have been linked to the Boston Marathon bombing a day earlier

The FBI is investigating a ‘military-style’ attack on a California electric power facility earlier this year.

The April 16 attack saw as many as two gunmen storm the PG&E Metcalf substation after severing phone service and fire several dozen rounds at transformers.

Federal officials took over the investigation from local law enforcement on fears it was linked to the Boston marathon bombing only a day earlier, but those fears appear to have subsided.

At least one person, maybe two, went down multiple manholes at the facility in a San Jose suburb and cut fiber cables leading to the substation, according to Foreign Policy, which detailed the well-planned attack.

Attacked: The FBI is investigating an April attack on PG&E's Metcalf substation. Experts have warned the assault could have been a 'dress rehearsal for a larger attack'

This knocked out 911 and landline service o the substation, as well as cell phone service to the surrounding area.

PG&E employees had no means to call for help when, at 1am, as many as two gunmen began their attack.

More than 100 rounds were fired from high-powered rifles at many transformers – 10 were damaged in one area and three transformer banks in another, a PG&E spokesperson told the site.

Cooling oil leaking from at least one transformer bank caused transformers to overheat and shut down. This led officials to warn locals to conserve energy, but no major power outages occurred.

No major damage or injuries were sustained either, but a stalled local investigation led the feds to take over the case.

Cables cut: At least one suspect cut communications cables along this highway and another before shooting up the substation

No major damage: Transformers were shot at over 100 times, but no serious damage was sustained, nor was anyone injured

‘Initially, the attack was being treated as vandalism and handled by local law enforcement,’ a senior intelligence official told Foreign Policy.

‘However, investigators have been quoted in the press expressing opinions that there are indications that the timing of the attacks and target selection indicate a higher level of planning and sophistication,’ the official explained.

The FBI was initially worried that the attack was somehow linked to the April 15 Boston Marathon bombing, but further investigation showed it to likely be an isolated local event, an agency spokesperson told Foreign Policy.

A PG&E official disagreed with that assertion, and told Foreign Policy the attack was ‘not amateurs taking potshots… this was a dress rehearsal.’

Lit up: The Santa Clara Sheriff's Office released this surveillance footage of the attack which shows the gunshots going off on the grounds of the PG&E facility

Sparks flew: No one was injured and the power didn't actually go out in the area because the state grid was able to maintain it but officials fear that it was a test run

The agency is following a couple of leads, but has yet to name any suspects. No one has claimed responsibility.

The FBI is also investigating a series of attacks on the Arkansas power grid where multiple high-voltage transmission lines were severed and one substation was set on fire, according to the New York Times.

‘You should have expected U.S.’ was scribbled on a control panel at the torched substation.