“Benefits that were once reserved for the career force were extended to even the lowest soldier,” said Jennifer Mittelstadt, a professor of history at Rutgers University who has taught courses at the Army War College on the military’s changing social contract. “There was a broad shift toward making life for the soldier more palatable, and pizza is part of that,” she said.

M.R.E.’s, introduced in the early 1980s to replace canned field rations, come in a tough plastic pouch and are meant to supply a complete 1,200-calorie meal, including snacks, dessert and instant coffee. All M.R.E.’s also come with a flameless ration heater activated by adding water to a chemical pouch. The pouches also include items like toilet paper, matches and chewing gum that may be hard to come by in the field.

Soldiers have always groused about their chow, of course. Generations of generals have repeated the adage that armies march on their stomachs, but few ever mentioned taste buds. As American military rations evolved from the salt pork and hardtack of the Civil War to Vietnam-era cans of ham and lima beans, the verdict of the troops remained reliably grim.

It was only during the first major field deployment of M.R.E.’s, during the Gulf War in 1991, that military leaders realized the monotonous and largely brown rations could become a morale problem. After the war, Gen. Colin Powell, the chairman of the Joint Chiefs of Staff, summoned the head of the Combat Feeding Directorate and gave him a two-word order: “Fix it.”

The directorate responded by scrapping its top-down system of developing rations in favor of a strategy it called “soldier requested, soldier tested, soldier approved.”

Food scientists began following troops into the field, not just to ask them what they liked and disliked, but also to dig through the trash to see what the troops actually ate.