Chances are you didn’t hear about it when it happened or the investigation that followed. Last April just outside of San Jose, California the grid system came under direct attack.

Investigators have yet to identify any suspects, but the attack seems to have been well planned. First, someone accessed an underground vault housing fiber optic telephone cables and cut off communications to a large PG&E Substation.

Then, for 19 minutes, someone opened fire from long-range.

The sniper apparently utilized 7.62x39mm rounds, such as those used in an AK-47, to target the oil-driven cooling systems for 17 large transformers. The shell casings found at the scene had been wiped clean of fingerprints. According to Newsmax none of the transformers exploded, but the damage was significant enough for PG&E to force their electricity feeds to reroute through another station in an effort to prevent a widespread blackout.