There are times like today-when the sky is clear, the sun is shining and enemy mortars are only falling about once every couple hours-that the requirement to always wear a helmet and flak vest seems a crime. Some Marines routinely flout the rule, but not Colbert. Suddenly, he stands up, throwing his helmet down, ripping off his flak vest and stripping down to his T-shirt. “You know what?” he announces. “I’m going to run through that field waving my arms like I’m an airplane.”

Colbert runs through the grass, making jet sounds, banks into a loose turn and flies back to his Humvee. He quickly dons his gear. “Better now,” he says, strapping his helmet on again.