This is the first in a three-part series titled “Your Brain on Energy” for our new Energy and Environment coverage. In the arid lands of the Mojave Desert, Marine regimental commander Jim Caley traveled alongside a 24-mile stretch of road and saw trucks, tanks and armored tracked vehicles all idling in the heat — and wasting enormous amounts of expensive fuel. Caley had already led forces in Iraq, and at the time was charged with seven battalions comprising 7,000 Marines. But this was a new and different challenge. Overseeing a major spring 2013 training exercise at the Marine Corps’ Twentynine...