Following the Irish War of Independence the Irish Free State was set up as an independent British Dominion covering most of the island of Ireland. After a brief civil war between the pro-Free State forces and members of the Irish Republican Army (IRA) who wanted any independent nation to cover the entire island the status of the Irish Free State was confirmed, and the IRA forced underground. The IRA had supporters in the United Kingdom, working openly as the Irish Self-Determination League (ISDL), and the Free State government shared the names of these supporters with the British authorities, who kept a close eye on them. Between February and March they provided information on individuals that they said were part of widespread plots against the Irish Free State being prepared on British soil. On 11 March 1923 the police in Britain arrested IRA sympathisers living in Britain including Art O'Brien, the head of the ISDL. Sources disagree on numbers, giving either approximately eighty or approximately 100. The arrested men were placed on special trains and sent to Liverpool, where they were transferred to Dublin via a Royal Navy destroyer. It later transpired that not only were many British citizens (Art O'Brien himself had been born in England), at least six had never even been to Ireland before.