and among mother countries and their colonies and dependencies before the dawn of the jet age. Such routes included Europe to African and Asian colonies, Europe to South America, and migrant traffic from Europe to North America in the 19th and first two decades of the 20th centuries, and to Canada and Australia after the Second World War. Shipping lines are companies engaged in shipping passengers and cargo, often on established routes and schedules. Regular scheduled voyages on a set route are called "line voyages" and vessels (passenger or cargo) trading on these routes to a timetable are called liners. The alternative to liner trade is "tramping" whereby vessels are notified on an ad hoc basis as to the availability of a cargo to be transported. (In older usage, "liner" also referred to ships of the line, that is, line-of-battle ships, but that usage is now rare.) The term "ocean liner" has come to be used interchangeably with "passenger liner", although it can refer to a cargo liner or cargo-passenger liner. The advent of the Jet Age and the decline in transoceanic ship service brought about a gradual transition from passenger ships to modern cruise ships as a means of transportation. In order for ocean liners to remain profitable, cruise lines modified some of them to operate on cruise routes, such as the . Certain characteristics of older ocean liners made them unsuitable for cruising, such as high fuel consumption, deep draught preventing them from entering shallow ports, and cabins (often windowless) designed to maximize passenger numbers rather than comfort. The Italian Line's and , the last ocean liners to be built primarily for crossing the North Atlantic, could not be converted economically and had short careers. History 19th century At the beginning of the 19th century, the Industrial Revolution and the inter-continental trade rendered the development of secure links between continents imperative. Being at the top among the colonial powers, the United Kingdom needed stable maritime routes to connect different parts of its empire: the Far East, India, Australia, etc. The birth of the concept of international water and the lack of any claim to it simplified navigation. In 1818, the Black Ball Line, with a fleet of sailing ships, offered the first regular passenger service with emphasis on passenger comfort, from England to the United States. In 1807, Robert Fulton succeeded in applying steam engines to ships. He