Ireland was a part of the UK during World War I. Five-sixths of the island left to form the Irish Free State, now the Republic of Ireland, in 1922. A total of 206,000 Irishmen served in the British forces during the war. The number of Irish deaths in the British Army recorded by the registrar general was 27,405. A significant number of these casualties were from what, in 1920, became Northern Ireland. While 49,400 soldiers died serving in Irish divisions (the 10th, 16th and 36th), although not all of the men serving in these divisions were natives of Ireland and many Irish who died in non-Irish regiments are not listed. For example, 29% of the casualties in the 16th Division were not natives of Ireland. Neither does it include Irish emigrants in Britain who enlisted there and are not categorised as Irish. Australia lists 4,731 of its first World War soldiers as having been born in Ireland and more than 19,000 Irish-born soldiers served in the Canadian Corps. According to research done by John Horne of Trinity College Dublin, there are at least 30,986 soldiers who were born in Ireland that died; however, that's considered a "conservative" estimate and is very likely to raise.