The development of the "Three Towns" (Plymouth, Devonport and Stonehouse) at the mouth of the river offered an important market for the valley's agricultural produce, needed in particular to serve the victualling requirements of the royal dockyard, and this was always carried by boat. In 1820 or 1821 the first paddle steamer on the Tamar inaugurated a service between Calstock and Devonport to deliver foodstuffs. In 1859 a rail connection from Plymouth to London was opened, and fresh produce could be landed at the Devonport steamer quays in the evening and be on sale in London by the next morning. The growing city population created a large demand for sightseeing cruises on the river and this was a significant source of traffic from 1823, with the launch of the Cornish steam packet "Sir Francis Drake", until the outbreak of the second world war.