Military nutrition has evolved over time. In the past, armies lived off the land, by pillaging food of the people whose land the army occupied, or requisitioning it. Often more soldiers died of disease that was exacerbated by malnutrition than from combat.
"An army marches on its stomach", said Napoleon Bonaparte, in the oft-quoted phrase.
In response to the need for food for the Grand Army that invaded Russia under Napoleon, a French government reward prompted Nicolas Appert to invent "canning", resulting in the first preserved food for armies (military rations), that came as food stuffed into wine bottles and then boiled to preserve it.
In the 19th century, British military tinned rations used tins that were sealed with lead solder. This led to cases of lead poisoning.