Plymouth has a long been used as a naval base. From the towns sheltered waters such famous seaman as Drake and Raleigh sailed. Devonport Dockyard started life in 1693 when a wet and dry dock was constructed, in what is now part of the South Yard. From these meagre beginnings the dockyard grew into the biggest naval base in Western Europe. It covers an area of some 622 acres, contains 25 tidal basins, 5 basins and 12 dry docks of varying sizes that can accommodate frigates, submarines and the through deck cruisers. Until the A and T class submarines of the 2nd Submarine Squadron and their depot ship HMS Forth arrived in Devonport in 1961 there had not been a submarine squadron based in Plymouth since the end of the First World War. Although submarines were far from a strange sight, the Dockyard built many submarines over the years of various classes.