The Thursday before Sandy made landfall, Thomas Creamer, Army Corps of Engineers chief of operations for the New York district, touched base with other districts that might be needed. The storm was not predicted to exceed Category 1 levels. But Creamer's job was to consider all possible options. It was "part of what we were doing just in case something went wrong," he says. "And it went wrong."

Preparing for the worst even when it was not supposed to happen proved key to the Corps' mission, which removed some 500 million gallons of floodwater from New York City infrastructure in less than a fortnight. The Corps dubs the effort "unwatering" rather than "dewatering" because the former more strongly implies the water was not supposed to be in that location to begin with.