Iron Rations

I remember watching an old BBC science series on (the old) TLC (ether Connections or The Day the Universe Changed) where it talked about how canned food in the Napoleonic Wars brought fourth modern food preservation. The need for canned food was due to mason jars being a bitch to transport and forging was not always viable.

An "iron ration" back then was a big-ass metal can of tin or wrought-iron that had to be pried-open by bayonet and rock. You could have a wide range of food in a can, with pre-cooked beans, vegetables and meat being typical, but the soldiers still had to cook the food, and the metal can could be heated for that use. Although, it was not perfect, as small leaks form to spoil the whole can, seals in the seamers (end-caps) contained lead, and, as noted, opening them is a real pain in the ass!

And yes, they still had dried food, with the hard-ass hardtack biscuit being the common staple. (Unless you want to "shit a brick" in a literal way, you're supposed to soak the biscuit in soup, stew or broth before eating it.)

As an armies marches on their stomachs, the iron ration was truly a "can of whoop-ass!"