Hard tack is a cracker/biscuit flat-bread used during long sea voyages and military campaigns before the introduction of canning as a primary food-source. Mostly inedible for dry and hard preservation, it was usually dunked in water, brine, coffee, or other liquids, or cooked into a skillet meal. This cracker was little more than flour and water which had been baked hard and would keep for months as long as it was kept dry. Also known as a sea biscuit, sea bread, or ship's biscuits.
Optional/not traditional adjustment: This will make the crackers more palatable but mean that unlike traditional hard bread they will eventually spoil, even if properly stored.
- 1 tablespoon of shortening
- Mix all the ingredients into a dough and press onto a cookie sheet to a thickness of ½ inch.
- Bake in a preheated oven at 400°F (205°C) for half an hour. Don't cut now
- Remove from oven, cut dough into 3-inch squares, and punch four rows of holes, four holes per row into the dough (a fork works nicely).
- Flip the crackers and return to the oven for another half hour.
Notes, tips, and variations 
- Some recipes also recommend a second baking at 250°F (120°C) to thoroughly dry out the bread.
- Scale ingredient quantities equally if more dough is required.