The lowest tier of casks stowed in the holds of a ship. In the US Navy they were always water casks with the largest sizes near the ship's centre of gravity. Before the days of refrigeration and freshwater tanks, most of the provisions carried for a voyage had to be carried in casks, and in view of the very long periods during which a sailing ship might remain at sea in those days, sufficient provisions for six months were usually carried. Several tiers of casks were necessary to carry this amount, and they were known as ground, second, third, etc., to the top tier.
Subjects: Maritime History.