Cunard's steamships left on the date, not when full, and made Atlantic shipping reliable

Before the transatlantic steamship was a regular service, a crossing was a gamble. Ships sailed when they had enough paying cargo and passengers, so the departure date was a matter of when bookings were full, and nothing could be planned around it.

In May 1839 Samuel Cunard, in partnership with George Burns and David MacIver, won a contract with the British government to provide a scheduled transatlantic steamship service carrying mail — the first of its kind. On 4 July 1840 the 1,156-ton paddle steamer Britannia left Liverpool and arrived in Halifax on schedule just ten days later.

Within a year the Britannia and her three sister ships together provided the first timetabled weekly steamship service across the Atlantic. The company was obliged to sail on the advertised date whether or not the hold was full, and that commitment, not the machinery alone, was what made the line reliable.

Because the sailing date could be trusted, the mail service and eventually first-class passengers and perishable freight began to plan around it. The scheduled crossing became a utility rather than an expedition, and the 'line' with a timetable was the product.