Hardtack
From Cookipedia
Hardtack (or hard tack) is a simple type of cracker or biscuit, made from flour, water, and sometimes salt. Inexpensive and long-lasting, it was and is used for sustenance in the absence of perishable foods, commonly during long sea voyages and military campaigns. The name derives from the British sailor slang for food, "tack". It is known by other names such as pilot bread (as rations for ship's pilots), ship's biscuit, shipbiscuit, sea biscuit, sea bread (as rations for sailors) or pejoratively "dog biscuits," "tooth dullers," "sheet iron" or "molar breakers". Australian military personnel know them as ANZAC wafers.