During the Second World War Denmark was invaded and occupied by Nazi Germany. The British subsequently made a pre-emptive invasion and occupation of the Faroes, known as Operation Valentine, to prevent a German invasion. Given their strategic location in the North Atlantic, the Faroes could have proved useful to Germany in the Battle of the Atlantic, possibly as a submarine base. Instead, the British forces built an airbase on Vágar, which is still in use as Vágar Airport. Faroese fishing boats also provided a large amount of fish to the UK, which was crucial given food rationing.