From the Northern Isles they continued to raid Scotland and Norway , prompting Harald HÃ rfagre to raise a large fleet which he sailed to the islands . In about 875 he and his forces took control of Shetland and Orkney . In response , Norwegian king Harald HÃ rfagre ( `` Harald Fair Hair '' ) annexed the Northern Isles ( comprising Orkney and Shetland ) in 875 .