After the independence of the Irish Free State on December 6 1922, three deep water Treaty Ports, at Berehaven, Queenstown (renamed Cobh) and Lough Swilly, were retained by the United Kingdom as sovereign bases. This was a condition of the Anglo-Irish Treaty of December 6 1921, which ended the Irish War of Independence.

The existence of the ports was one of the causes of the Irish Civil War, where those who regarded the Treaty as a betrayal of Irish Republicanism fought against the forces of the nascent Free State.

The ports remained under the control of the UK until Anglo-Irish Free Trade Agreement in 1938, when they were returned to Éire. From an Irish point of view, the handover of the ports in the leadup to World War II was vital to establish Ireland's neutrality during "The Emergency".

Some in Britain considered the handover a short-sighted decision, since at the start of the Battle of the Atlantic in 1939, the convoy escort refuelling facilities which Berehaven and Queenstown would have provided were 370 kilometres (200 miles) further out into the Atlantic than those which were available in Northern Ireland and Great Britain. This became less important after the Allies established bases in Iceland following the British occupation in 1940. Moreover, the ports had been neglected by the British Admiralty and would not have been ready for war.