There’s an old war story about a G.I. who attended a USO show where one of the acts was a man who consumed unusual items. As the audience watched, the entertainer chewed glass, gobbled nails and even swallowed swords.

Unperturbed by the spectacle, the soldier turned to a friend sitting next him and asked, “But can he digest C-rations?”

Relished and reviled, C-rations fed millions of troops in the field. The iconic green cans were far from home cooking, but they did sustain a fighting man when he was far from home—or at least the mess hall—until 1981, when they were replaced by the Meal Ready to Eat, or MRE.

“If you were in the field, hungry and you could heat them up, they were great—slightly better than shoe leather,” Dick Thompson, vice president of the Vietnam War Foundation & Museum in Ruckersville, Virginia, and a retired U.S. Army lieutenant colonel, told War Is Boring. “If you were in garrison where you had a choice, forget about it!”

Napoleon once said an army marches on its stomach. In other words, poorly fed troops fight poorly—food is a force multiplier.

But food preservation for long periods of time and the logistics of moving food to troops on the battlefield are two of warfare’s oldest challenges.

The U.S. military is no different. During the 1930s, the War Department did its best to develop several kinds of compact, long-lasting rations that could feed men in combat.

One was the C-ration, first issued in 1939. It was three cans of different meat and vegetables—field manuals of the time described the contents as having “the taste and appearance of a hearty stew”—and three cans containing crackers, instant coffee and sugar.

It wasn’t Mom’s home cooking, but it was filling. Each complete C-ration contained about 2,900 calories and sufficient vitamins to keep the troops healthy.

C-rations were just one of the letter-coded rations the military issued during World War II. Most soldiers and Marines from that time remember—and detest—the K-rations of the era, which had three separate meal units for breakfast, lunch and dinner.

During the Korean War, C-rations soon eclipsed the K-ration as the most commonly issued field ration.

But the food was boring—“menu fatigue” was the term military dieticians used.

In 1958, the Defense Department created 12 different menus. Each menu contained one canned meat item; one canned fruit, bread or dessert item; one “B unit” that contained items such as crackers and chocolate; an accessory packet containing cigarettes, matches, chewing gum, toilet paper, coffee, creamer, sugar, and salt; and a spoon.