Colonel Geoffrey Ling, a neurologist with the Defense Department, had come to the InterContinental to share some of the government’s research with the N.F.L.’s medical brain trust. (Concussions among the men and women returning from Iraq and Afghanistan, one doctor told me, could be “the next Agent Orange.”) “If you look historically, what really hurts our soldiers from blasts is artillery shells, mortar shells,” Ling said. “The combat helmet was designed particularly for mitigation of fragments. It does have some ballistic protection. You could shoot at the thing point blank with a 9-millimetre pistol, and you won’t penetrate it. That’s pretty doggone good. I’m surprised New York City policemen aren’t wearing the doggone thing. But, like, I wouldn’t play football with the thing. It ain’t that good.”