"Hardtack" or "Sea Biscuit" or "Pilot Bread" was a standard food for sailors, soldiers, and travelers. It had to be nutritious, compact, durable enough to withstand bumps during transport, with minimum spoilage even over an extended period. Flavor and texture were secondary.
Modern recipes call for "flour", water, and salt. (That IS what was in the old recipes.) However, these new recipes date from after fast steam boats, fast trains, and more importantly massive changes in agriculture, flour milling, and baking circa 1870.
After 1870, agriculture produced pure cultivars of grain, roller milled into white flour, mixed into doughs in mechanical mixers, and baked in mechanical ovens. Prior to ~1870 grain was produced in "land races" which resulted in a variety of grains mixed together, that was stone ground into "flour". Thus, "flour" from 1850 was very different from the flour of 1890. Dough in 1850 (and prior) was likely mixed by hand (or foot) in wooden troughs - where it picked up a sourdough start - whether mentioned in the recipe or not.
Thus, my recipe for hardtack is a mix of soft wheat, red wheat, barley, spelt, oats, rye and malted grain; all stone ground to flour. I dissolve an active sourdough starter in water, and mix a very soft dough. I mix in salt, and let sit on the kitchen counter overnight. I use a food scoop to place small balls of the dough on oiled parchment paper on a bake sheet, and use a wet bench knife to spread out to 1/8" inch thick. I cover with an inverted bake sheet, and allow to rise until double in thickness. I use my wet bench knife to cut in squares, and a wet fork to prick. Bake 375F convection until dry. Dip in coffee or grog or soup if you actually intend to eat it.
Modern hardtack made from white flour, keeps much better. However, you would not want to try and live on hardtack made from white flour during a long sea voyage.