I'm betting it was like granny's hardtack. If you steamed it, it wasn't bad, or of you soaked it in soup, you could even fry it, it had a salty, buttery kind of thing going on with a hint of library paste. No I'm serious. I'm not sure you can even get the ingredients she used anymore. It was 1/2 flour and half hominy corn meal, and chunky salt mixed in boiling water, pressed flat, and dried over the wood stove FOR DAYS! there was a variation that you had to keep cool because it had molasses or brown sugar in it, We got them to teeth on as kids and the taste was good enough we kept gnawing them. Yet another variation had dried veggies in it and you just poured hot water on a broken-up hunk and made a porridge.
My late lovely Mary had this thing she called "Day bread" Her family used it as lunch in the log woods of Seattle. It had flour, cornmeal, mashed potatoes onion, eggs, and bacon or jerky in it, and was crust fried in bacon grease. a pone of that was not only good tasting, but it would last several days even in hot weather. they used to just wrap it up in a do-rag or towel before they went to cut wood. It was a nuclear bomb in white bean soup!
Oh yeah, G.I issues. Well, if you supplement other foods like stew or beans with them, or make a soup directly, very few, greens and vegetable-based diets especially. BUT if you ate it by itself for several days, the result is much like giving birth to a cinder-block! The day bread, not so much, but hard tack...You might want to drink a LOT of water and bring a hunk of water hose to gnaw on, it's not going to be pretty!
I'll work on the bannock and let you know.