Grimsby Haven Act) for the purpose of "widening, deepening, enlarging, altering and improving the Haven of the Town and Port of Great Grimsby". After the dredging of The Haven and related improvement in the early 19th century, the town grew rapidly as the port boomed, importing iron, timber, wheat, hemp, and flax. New docks were needed to cope with the expansion. The necessary works were allowed under the Grimsby Docks Act of 1845. The arrival of the railway in 1848 eased the transport of goods to and from the port to markets and farms. Coal mined in the South Yorkshire coalfields was brought by rail and exported through Grimsby. Rail links direct to London and the Billingsgate Fish Market allowed fresh "Grimsby fish" to gain nationwide renown. The first true fish dock opened in Grimsby in 1856, and the town became central to the development of the commercial fishing industry. The Dock Tower was completed in 1851, followed by the Royal Dock in 1852. No.1 Fish Dock was completed in 1856, followed by No.2 Fish Dock in 1877. Alexandra Dock and Union Dock were completed in 1879. During this period, the fishing fleet was much expanded. In a rare reversal of usual trends, large numbers of fishermen from the south-east and Devon travelled north to join the Grimsby fleet. Over 40 per cent of the newcomers came from Barking in East London and other Thames-side towns. In 1857 there were 22 vessels in Grimsby. Six years later there were 112. The first two legitimate steam trawlers built in Britain were based in Grimsby. By 1900, a tenth of the fish consumed in the United Kingdom was landed there, although there were also many smaller coastal fishing ports and villages involved. The demand for fish in Grimsby meant that at its peak in the 1950s it claimed to be the largest fishing port in the world. The population grew from 75,000 in 1901 to 92,000 by 1931. The Great Depression and restructured fishing caused a sharp decline in employment. After that the population was fairly stable for the rest of the 20th century. Second World War The Royal Dock became the UK's largest base for minesweepers patrolling the North Sea. The Admiralty requisitioned numerous trawlers to serve the purpose of the Royal Naval Patrol Service. Often the crew was ex-trawlermen, alongside Royal Naval Reserve and Royal Navy volunteers. Trawlers used the