 During the 18th century, ships carrying cargo, passengers and mail between Europe and America would sail only when they were full, but in the early 19th century, as trade with America became more common, schedule regularity became a valuable service.Starting in 1818, ships of the Black Ball Line began regularly scheduled trips between Britain and America.These "packet ships" (named for their delivery of mail "packets") were infamous for keeping to their disciplined schedules.