 Once dominant export orientated manufacturing industries such as shipbuilding and other heavy engineering have been gradually replaced in importance by more diversified forms of economic activity, although major manufacturing firms continue to be headquartered in the city, such as Aggreko, Weir Group, Clyde Blowers, Howden, Linn Products, Firebrand Games, William Grant & Sons, Whyte and Mackay, The Edrington Group, British Polar Engines and Albion Motors.Glasgow was once one of the most significant cities in the UK for manufacturing, which generated a great deal of the city's wealth; the most prominent industry being shipbuilding based on the River Clyde.Although Glasgow owed much of its economic growth to the shipbuilding industry, which still continues today in the form of BAE Systems Maritime - Naval Ships' two shipyards, the city has its roots in the tobacco trade and is noted to have "risen from its medieval slumber" from trade in tobacco, pioneered by figures such as John Glassford.