In 1904, in response to the build-up of the German "Kaiserliche Marine"'s High Seas Fleet, Britain decided that a northern base was needed to control the entrances to the North Sea, as part of a revised policy of 'distant' rather than 'close' blockade. First Rosyth in Fife was considered, then Invergordon at Cromarty Firth. Delayed construction left these largely unfortified by the outbreak of the First World War. Scapa Flow had been used many times for British exercises in the years before the war and when the time came for the fleet to move to a northern station, it was chosen for the main base of the British Grand Fleet—unfortified.