Anglo-Irish relations in the 20th century can be described as being close but tortuous. This paradox is fused with Ireland's geographical: both isolation from Europe and proximity to the main island of the British archipelago. Using a geopolitical analysis, based on the theories of Sir Halford MacKinder, this text offers an understanding of the strategic imperatives that have driven British policy throughout the events of the 20th century. It presents a different perspective on the reality of Irish neutrality, and the importance of Northern Ireland in the Battle of the Atlantic during the Second World War. Furthermore, using US archival material, it gives an insight into Ireland's geopolitical importance in the First World War, and her contribution to victory against the German U-boats.