Ship biscuit is a type of hard, unleavened biscuit that was commonly used as a staple ration on long sea voyages. There are several synonyms for ship biscuit such as hardtack, sea biscuit, hard bread, pilot bread, and navy bread. Hardtack is the oldest term which was used as a ration in ancient times as well. Sea biscuits and pilot bread were specifically made for sailors, while hard bread and navy bread were often used in military rations. All of these terms refer to a dense, long-lasting, and easily storable type of biscuit that was ideal for traveling and preserving food in the days before refrigeration.