No. 4 Operational Training Unit (4OTU) was an operational conversion unit of the Royal Australian Air Force during World War II. It was formed on 1 October 1942 and located at RAAF Base Williamtown, New South Wales. 4OTU operated Vultee Vengeance and CAC Wirraway aircraft. It was disbanded on 30 April 1944, handing Williamtown over to a detachment of No. 5 Operational Training Unit the following day.