Hartack (or hard tack) is a simple type of cracker or biscuit, made from flour, water, and salt. Inexpensive and long-lasting, it is and was 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 bush pilots) , ship's biscuit, sea biscuit, sea bread (as rations for sailors) or pejoratively "dog biscuits", "tooth dullers", "sheet iron" or "molar breakers".