Soldiers: Your underwear of the future will do more than prevent crotch rot. It’ll protect you from injuries, monitor your vitals, and even “harvest” your energy. That is, if a new project from Darpa’s Defense Sciences Office works out as planned. That’s an illustration, to the right, of what Darpa thinks its “Warrior Web” onesie might look like.

So far, the project is still in the draw-a-cartoon-with-a-six-pack-in-tights stage — a long way off from the “adaptive, compliant, nearly transparent, quasi-active joint support suit,” which can “mitigate musculoskeletal injury caused by discrete dynam...