PETERBOROUGH, England — Helmand province's shades of yellow, cookies wrapped in pink foil and southern Afghanistan's sweaty heat have imprinted on Lance Cpl. Cassidy Little's mind. But then his memory of that day in May 2011 fractures. One moment he was walking through an unsecured compound with his patrol, the next he was on his back, staring into swirling dust and black smoke, his body unresponsive. He had been hit by the blast from an improvised explosive device , buried underground for