What happened

Attackers cut fiber-optic communications cables in an underground vault, then fired more than 100 rounds from at least two high-powered rifles at Pacific Gas & Electric's Metcalf transmission substation near San Jose, disabling 17 transformers and causing more than $15 million in equipment damage. Grid operators avoided major disruption by rerouting power remotely, and PG&E spent 27 days repairing the site. Former FERC chairman Jon Wellinghoff called it, per a Wall Street Journal investigation, "the most significant incident of domestic terrorism involving the grid that has ever occurred" in the US at the time. The attack prompted the industry's first major push on substation physical security and led the Federal Energy Regulatory Commission to approve the CIP-014 critical-infrastructure-protection standard in November 2014.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.