“SO VAST IS the [Department of Defence] and so multifarious are its missions,” wrote Ash Carter, America’s 25th secretary of defence, “that it dwarfs most institutions on Earth.” He was not exaggerating. The Pentagon owns or maintains almost 30m acres of real estate, he noted, an area larger than the state of Pennsylvania. Its carbon emissions are about 1% of the country’s total. Its annual budget, a little over $800bn, exceeds the GDP of Taiwan, Belgium or Argentina. It is the largest buyer of fuel, the largest owner of ships and among the largest employers on the planet. On January 20th, should he be confirmed by the Senate, Pete Hegseth, a Fox News presenter and former infantry platoon leader, will inherit this sprawling apparatus. What does the job involve?