Yarrow Shipbuilders Limited (YSL), often styled as simply Yarrows, was a major shipbuilding firm based in the Scotstoun district of Glasgow on the River Clyde. It is now part of BAE Systems Surface Ships, owned by BAE Systems, which has also operated the nearby Govan shipyard since 1999.

A high pressure watertube boiler is a type of boiler in which water circulates in tubes heated externally by fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate steam.