A new Wall Street Journal report is calling attention to an incident that occurred last April that many Americans may not be aware of.

'Death Toll Would Be Staggering': Judge Jeanine Warns About Attack on Power Grid

Here's a portion of the story:

SAN JOSE, Calif.—The attack began just before 1 a.m. on April 16 last year, when someone slipped into an underground vault not far from a busy freeway and cut telephone cables.

Within half an hour, snipers opened fire on a nearby electrical substation. Shooting for 19 minutes, they surgically knocked out 17 giant transformers that funnel power to Silicon Valley. A minute before a police car arrived, the shooters disappeared into the night.

To avoid a blackout, electric-grid officials rerouted power around the site and asked power plants in Silicon Valley to produce more electricity. But it took utility workers 27 days to make repairs and bring the substation back to life.

Nobody has been arrested or charged in the attack at PG&E Corp.'s Metcalf transmission substation. It is an incident of which few Americans are aware. But one former federal regulator is calling it a terrorist act that, if it were widely replicated across the country, could take down the U.S. electric grid and black out much of the country.

The attack was "the most significant incident of domestic terrorism involving the grid that has ever occurred" in the U.S., said Jon Wellinghoff, who was chairman of the Federal Energy Regulatory Commission at the time.

Some are now questioning whether this could have been a test run and expressing concern that the perpetrators could strike again. The FBI is continuing its investigation, but doesn't believe a terror organization was responsible.

Jenna Lee discussed the alarming situation with Chad Sweet, former chief of staff for DHS Secretary Michael Chertoff. He called it a "sophisticated" attack, but believes it's still premature to label it as terrorism.

Lee pointed out that one reason the incident didn't get national attention was because PG&E was able to avoid blackouts by working around the downed transformers. She asked Sweet how prepared the industry is overall to deal with something like this.

Sweet said it's encouraging that there was no large-scale outages, adding that it shows power companies have plans in place to maintain power.