A little-reported attack on a power substation in California last year wasn't vandalism, but the "most significant incident of domestic terrorism involving the grid that has ever occurred" in the US, according former top power regulator Jon Wellinghoff. In the assault in South San Jose last April, unknown attackers severed underground cables at a substation before snipers knocked out 17 transformers in 19 minutes, the Los Angeles Times reports.
Wellinghoff, who was chairman of the Federal Energy Regulatory Commission at the time, warns that the attack was well-planned and carried out by people who knew what they were doing—and similar attacks on the nation's poorly protected power infrastructure could cause huge blackouts across the country, reports the Wall Street Journal. Grid operators had to scramble to avoid a blackout after the San Jose attack, which Wellinghoff suspects was a trial run. The FBI, however, says it doesn't believe the attack was terrorism—though it hasn't been ruled out as a motive.