Clement Atlee - that wouldn't quite be correct. There are three dates regarding the devolution of power to Ireland, not just two.
1922 - Irish Free State created, it becomes a dominion within the Commonwealth
1937 - Ireland is no longer a
Commonwealth Realm and becomes a Republic - the Republic of Ireland
1949 - Ireland leaves the
British Commonwealth all together
Commonwelath Realms are nations that continue to have the British Monarch as their monarch, despite being independent. Being a member of the British Commonwelath, now known as the Commonwealth of Nations, is just when you are in the organisation called the Commonwealth, but British customs aren't integrated into the nation's own constitution(s).
1949 was just when Ireland left the organisation, but it lost the monarchy back in 1937.
http://en.m.wikipedia.org/wiki/Irish_Free_State
Edited 4/5/2015 21:15:40