In 1937, the United States Army approached Hershey's Chocolate with one of the strangest product briefs in food history.

They wanted a chocolate bar, but they needed it to taste, in the words of the Army Quartermaster himself, "only a little better than a boiled potato."

Captain Paul Logan of the US Army Quartermaster General's office sat down with Hershey's chief chemist Sam Hinkle and laid out four requirements for what would become the Field Ration D bar. It had to weigh four ounces. It had to be high in energy. It had to withstand high temperatures without melting. And it absolutely could not taste good. The Army's logic was straightforward: if the emergency ration chocolate was delicious, soldiers would eat it whenever they wanted rather than saving it for genuine emergencies. The solution was to engineer the palatability out of it on purpose.

Hinkle and his team spent months developing the formula. They reduced the sugar dramatically. They increased the chocolate liquor to make it more bitter....