sentences:  O'Neill joined the British Army as a second lieutenant in the 2nd Regiment of Life Guards on 26 May 1897, and was promoted to lieutenant on 15 June 1898.He saw active service in South Africa between 1899 and 1900, during the Second Boer War, for which he was awarded the Queen's South Africa Medal with three clasps.On 3 January 1902 he was promoted to captain, and temporary appointed adjutant to the 2nd Life Guards.