hardtack

noun

1. (countable, uncountable)A large, hard biscuit made from unleavened flour and water; formerly used as a long-term staple food aboard ships.

   “Meronym: reefer's nut”

   “Philander went into the next room[…]and came back with a salt mackerel that dripped brine like a rainstorm. Then he put the coffee pot on the stove and rummaged out a loaf of dry bread and some hardtack.”

   “Bread and fodder had to be brought up over longer and longer distances, it was more difficult all the time, transport was lacking, the army had already eaten two-thirds of its hardtack, exhausted men were marching in baking heat along sandy roads into emptiness!”