Pilot bread

Hardtack is a type of dense biscuit (British English) or cracker (American English) made from flour, water, and sometimes salt. Hardtack is inexpensive and long-lasting. It is used for sustenance in the absence of perishable foods, commonly during long sea voyages, land migrations, and military campaigns. Along with salt pork and corned beef, hardtack was a standard ration for many militaries and navies from the 17th to the early 20th centuries. The name is derived from "tack", the British sailor slang for food. The earliest use of the term recorded by the Oxford English Dictionary is from 1830. It is known by other names including brewis (possibly a cognate with "brose"), cabin bread, pilot bread, sea biscuit, soda crackers, sea bread (as rations for sailors), ship's biscuit, and pejoratively as dog biscuits, molar breakers, sheet iron, tooth dullers, armor plates (Germany) and worm castles. Australian and New Zealand military personnel knew them with some sarcasm as ANZAC wafers (not to be confused with Anzac biscuit).

Source: Wikipedia