The Treaty included provisions by which the British would retain sovereignty over three strategically important ports known as the Treaty ports, one of which being described in the Treaty as:[6] Lough Swilly (d) Harbour defences to remain in charge of British care and maintenance parties.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.

The ceremony was brought forward from October 26, the date originally fixed under the Anglo-Irish Pact, on account of the international situation.

When the British troops left last evening en route for Shoeburyness, their new headquarters, they were given a cordial send off.

The guns at the Fort were manned by the Irish Army until decommissioned following the Second World War.