I made some out of white flour, water, and salt. It was basically inedible when dry, hard as a brick and had to be soaked in something edible to eat it. I saw on one of those WW 2 shows where they cooked it in fat to make it edible.
It will last forever. They ate it in WW 1 and possibly 2 because it was portable and lightweight.
By the time of WWI they had changed dramatically from what they were in the AWI or before, and up to the Civil War.
The flour they used is what we today call,
whole wheat pastry flour. Today's flour is from hard, red wheat, while there's was from what we call soft, white wheat. Further, it was the lowest grade flour, called "ship's stuff", which had a lot of bran. So, IF you want to try something closer to what they ate in the 18th century, use whole wheat pastry flour, AND 1/3 of it should be
wheat bran. So...,
Flour with wheat bran and water, and nothing else. No honey, no sugar, no oil or fat, no salt...., rolled into 1/4 thick paste and cut with a biscuit cutter, or larger, and poked with holes, then dried in a 200 degree oven overnight.
Yeah they are hard but you can eat them plain, though sometimes you have to suck on them a minute or two. I've got a test batch in the basement in a tin...three years old and not moldy yet.
LD