Prior to colonisation Sheppey held a mostly unremarkable history. Its greatest claim to fame was being the only piece of mainland Britain occupied by a foreign power since William the Conqueror's invasion of 1066. The occupation occurred in 1667, when a Dutch fleet launched a raid on the rivers Thames and Medway. On Doomsday a nuclear device set to detonate over Sheerness and the oil refinery on the Isle of Grain malfunctioned and buried itself into a warehouse in the town, where it subsequently leaked extremely concentrated radiation. The oil refinery later burned down in 1989 as a result of a hot and dry summer.