ship’s biscuit or hard tack or sea biscuit a type of unleavened bread which was baked, sliced, and oven dried. Thus it was ‘twice-cooked bread’, the meaning of the medieval Latin term panis biscoctus, from which comes the word biscuit.
This product was used for centuries as rations for sailors. In good conditions it would keep for a year or more in sealed barrels, but at sea it was often difficult to keep it dry, and it could become infested by weevils.
A special bakery at the royal docks at Chatham was devoted entirely to baking ship’s biscuit for the Royal Navy. The method was unchanged for several centuries. The Encyclopaedia Britannica of 1773 gave the following description:
Sea-bisket is a sort of bread much dried by passing the oven twice to make it keep for sea service. For long voyages they bake it four times and prepare it six months before embarkation. It will hold good for a whole year.