Lough Swilly has long been of immense historical significance.
The Norsemen and later the Ango-Normans and the mercenary soldiers, the Gallowglasses used the Swilly when coming to Ireland.
The Flight of the Earls, O'Neill and O'Donnell into exile took place from Rathmullan in September 1607.
Wolfe Tone was taken under naval arrest into Buncrana in 1798 and in more recent times during World War I, the Grand Fleet sheltered in the Lough. Near to the spot where Wolfe Tone was brought ashore in 1798 a small fort was erected to guard against the possible return of a French invasion fleet.
In the late 19th Century the fort was modernised and enlarged with the building of the, ‘Top Fort’ on Dunree Hill. During World War I it stood guard whilst Admiral Lord Jellicoe’s fleet anchored in Lough Swilly prior to engaging the German Navy at the Battle of Jutland. On 6 December 1921, the Anglo Irish Treaty was concluded.
The Irish Free State was established on 6 December 1922. The Treaty included provisions by which the British would retain sovereignty over three strategically important ports known as the Treaty ports.
Accordingly, even after the establishment of the Irish Free State, the Royal Navy continued to maintain its presence at Fort Dunree. Fort Dunree remained under British sovereignty until 3 October 1938 when, pursuant to the Anglo-Irish Trade Agreement of 25 April 1938, the territory was ceded to Ireland.