" He found several thick chocolate bars—probably Hershey’s military-issue Ration D bars—divided into segments and packaged in wax-dipped containers to resist gas attack. Designed to be unpalatably bitter so soldiers would eat them only in dire circumstances, they were formulated to be highly caloric and melt-resistant. "

― Laura Hillenbrand , Unbroken: A World War II Story of Survival, Resilience and Redemption