» “Sea biscuit” redirects here. For other uses, see Seabiscuit (disambiguation).:For the series of nuclear tests, see Operation Hardtack. Hardtack (or hard tack) is a simple type of cracker or biscuit, made from flour, water, and salt. Inexpensive and long-lasting, it's 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 s… (More on Hardtack)