You often hear about the threat of cyber attacks, or even EMP against the electric grid. But we don't realize how vulnerable it is to physical attack. The story linked below is interesting - I hadn't heard of it. Individuals broke into a substation, cut fibers and thus 911 services, and then fired 100+ rounds from automatic weapons into transformers. The transformers leaked and shut down due to overheating. Quite possibly a training run given the nature of the attack.