A detailed timeline of last April's deliberate attack on a power plant has been reconstructed by The Wall Street Journal, provoking questions about whether the event was a precursor to a much larger operation. At around 1:30 a.m. on April 16, 2013, snipers began shooting out transformers at the Metcalf substation.

John Wellinghoff, who chaired the Federal Energy Regulatory Commission at the time of the attack, described the incident to the Journal as "the most significant incident of domestic terrorism involving the grid that has ever occurred." Wellinghoff is going public with the details out of concern that a vulnerable power grid is a national security concern. A retired vice president for PG&E, which owns the Metcalf plant, also told the Journal that the attack was far from spontaneous or the work of a few reckless individuals.

During the 19 minutes of shooting, the gunmen knocked out 17 transformers, which then took nearly a month to repair. Prior to that they had cut telephone lines in a nearby underground vault, and according to the timeline, stopped shooting only a minute before police arrived.

Video released last June shows sparks flying as bullets hit the fence surrounding the transformers. Investigators recovered more than 100 casings at the site.

Foreign Policy covered the assault on the substation at the end of December, quoting retiring congressman Henry Waxman as having said, "It is clear that the electric grid is not adequately protected from physical or cyber attacks." The utility industry tends to focus its concerns on cyberattacks—hackers who can shut down the grid remotely—rather than the more old-school tactic of just shooting at transformers until they go boom.