From time to time Prime Ministers are required to leave the country on government business and a deputy acts in their place during that time. In the days before jet aircraft, such absences could be for extended periods. For example, William Watt was acting prime Minister for 16 months, from April 1918 until August 1919, when Prime Minister Billy Hughes was away at the Paris Peace Conference,[21] and Senator George Pearce was acting Prime Minister for more than seven months in 1916.[22] An acting Prime Minister is also appointed when the prime minister takes leave.